import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        String a = sc.next();
        String b = sc.next();
        String c = sc.next();
        char[] ca = a.toCharArray();
        char[] cb = b.toCharArray();
        char[] cc = c.toCharArray();
        int pos = 0;
        int i = 0;
        int j = 0;
        int k = 0;
        while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        }
    }
}

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    }

    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
        return hasNextByte();
    }

    public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main {
    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        String a = sc.next();
        String b = sc.next();
        String c = sc.next();
        char[] ca = a.toCharArray();
        char[] cb = b.toCharArray();
        char[] cc = c.toCharArray();
        int pos = 0;
        int i = 0;
        int j = 0;
        int k = 0;
        while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        }
    }
} Main public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        String a = sc.next();
        String b = sc.next();
        String c = sc.next();
        char[] ca = a.toCharArray();
        char[] cb = b.toCharArray();
        char[] cc = c.toCharArray();
        int pos = 0;
        int i = 0;
        int j = 0;
        int k = 0;
        while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        }
    } main {
        FastScanner sc = new FastScanner();
        String a = sc.next();
        String b = sc.next();
        String c = sc.next();
        char[] ca = a.toCharArray();
        char[] cb = b.toCharArray();
        char[] cc = c.toCharArray();
        int pos = 0;
        int i = 0;
        int j = 0;
        int k = 0;
        while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        }
    } FastScanner sc = new FastScanner(); sc new FastScanner() String a = sc.next(); a sc.next() sc.next sc String b = sc.next(); b sc.next() sc.next sc String c = sc.next(); c sc.next() sc.next sc char[] ca = a.toCharArray(); ca a.toCharArray() a.toCharArray a char[] cb = b.toCharArray(); cb b.toCharArray() b.toCharArray b char[] cc = c.toCharArray(); cc c.toCharArray() c.toCharArray c int pos = 0; pos 0 int i = 0; i 0 int j = 0; j 0 int k = 0; k 0 while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        } true {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        } if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            } pos == 0 pos 0 {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } if (i >= a.length()) {
                    System.out.println("A");
                    return;
                } i >= a.length() i a.length() a.length a {
                    System.out.println("A");
                    return;
                } System.out.println("A") System.out.println System.out System System.out "A" return; if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                } ca[i] == 'a' ca[i] ca i 'a' {
                    pos = 0;
                } pos = 0 pos 0 if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                } ca[i] == 'b' ca[i] ca i 'b' {
                    pos = 1;
                } pos = 1 pos 1 if (ca[i] == 'c') {
                    pos = 2;
                } ca[i] == 'c' ca[i] ca i 'c' {
                    pos = 2;
                } pos = 2 pos 2 i++ i if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            } pos == 1 pos 1 {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } if (j >= b.length()) {
                    System.out.println("B");
                    return;
                } j >= b.length() j b.length() b.length b {
                    System.out.println("B");
                    return;
                } System.out.println("B") System.out.println System.out System System.out "B" return; if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                } cb[j] == 'a' cb[j] cb j 'a' {
                    pos = 0;
                } pos = 0 pos 0 if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                } cb[j] == 'b' cb[j] cb j 'b' {
                    pos = 1;
                } pos = 1 pos 1 if (cb[j] == 'c') {
                    pos = 2;
                } cb[j] == 'c' cb[j] cb j 'c' {
                    pos = 2;
                } pos = 2 pos 2 j++ j {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            } if (k >= c.length()) {
                    System.out.println("C");
                    return;
                } k >= c.length() k c.length() c.length c {
                    System.out.println("C");
                    return;
                } System.out.println("C") System.out.println System.out System System.out "C" return; if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                } cc[k] == 'a' cc[k] cc k 'a' {
                    pos = 0;
                } pos = 0 pos 0 if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                } cc[k] == 'b' cc[k] cc k 'b' {
                    pos = 1;
                } pos = 1 pos 1 if (cc[k] == 'c') {
                    pos = 2;
                } cc[k] == 'c' cc[k] cc k 'c' {
                    pos = 2;
                } pos = 2 pos 2 k++ k String[] args args class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    }

    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
        return hasNextByte();
    }

    public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }
} FastScanner private final InputStream in = System.in; in System.in System System.in private final byte[] buffer = new byte[1024]; buffer new byte[1024] 1024 private int ptr = 0; ptr 0 private int buflen = 0; buflen 0 private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    } hasNextByte {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    } if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        } ptr < buflen ptr buflen {
            return true;
        } return true; true {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        } ptr = 0 ptr 0 try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } IOException e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                buflen = in.read(buffer);
            } buflen = in.read(buffer) buflen in.read(buffer) in.read in buffer if (buflen <= 0) {
                return false;
            } buflen <= 0 buflen 0 {
                return false;
            } return false; false return true; true private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    } readByte {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    } if (hasNextByte())
            return buffer[ptr++];
        else
            return -1; hasNextByte() hasNextByte return buffer[ptr++]; buffer[ptr++] buffer ptr++ ptr return -1; -1 1 private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    } isPrintableChar {
        return 33 <= c && c <= 126;
    } return 33 <= c && c <= 126; 33 <= c && c <= 126 33 <= c 33 c c <= 126 c 126 int c c public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
        return hasNextByte();
    } hasNext {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
        return hasNextByte();
    } while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++; hasNextByte() && !isPrintableChar(buffer[ptr]) hasNextByte() hasNextByte !isPrintableChar(buffer[ptr]) isPrintableChar(buffer[ptr]) isPrintableChar buffer[ptr] buffer ptr ptr++ ptr return hasNextByte(); hasNextByte() hasNextByte public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    } next {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    } if (!hasNext())
            throw new NoSuchElementException(); !hasNext() hasNext() hasNext throw new NoSuchElementException(); new NoSuchElementException() StringBuilder sb = new StringBuilder(); sb new StringBuilder() int b = readByte(); b readByte() readByte while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        } isPrintableChar(b) isPrintableChar b {
            sb.appendCodePoint(b);
            b = readByte();
        } sb.appendCodePoint(b) sb.appendCodePoint sb b b = readByte() b readByte() readByte return sb.toString(); sb.toString() sb.toString sb public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    } nextLong {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    } if (!hasNext())
            throw new NoSuchElementException(); !hasNext() hasNext() hasNext throw new NoSuchElementException(); new NoSuchElementException() long n = 0; n 0 boolean minus = false; minus false int b = readByte(); b readByte() readByte if (b == '-') {
            minus = true;
            b = readByte();
        } b == '-' b '-' {
            minus = true;
            b = readByte();
        } minus = true minus true b = readByte() b readByte() readByte if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        } b < '0' || '9' < b b < '0' b '0' '9' < b '9' b {
            throw new NumberFormatException();
        } throw new NumberFormatException(); new NumberFormatException() while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        } true {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        } if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            } '0' <= b && b <= '9' '0' <= b '0' b b <= '9' b '9' {
                n *= 10;
                n += b - '0';
            } n *= 10 n 10 n += b - '0' n b - '0' b '0' if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            } b == -1 || !isPrintableChar(b) b == -1 b -1 1 !isPrintableChar(b) isPrintableChar(b) isPrintableChar b {
                return minus ? -n : n;
            } return minus ? -n : n; minus ? -n : n minus -n n n {
                throw new NumberFormatException();
            } throw new NumberFormatException(); new NumberFormatException() b = readByte() b readByte() readByte public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    } nextInt {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    } long nl = nextLong(); nl nextLong() nextLong if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException(); nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE nl < Integer.MIN_VALUE nl Integer.MIN_VALUE Integer Integer.MIN_VALUE nl > Integer.MAX_VALUE nl Integer.MAX_VALUE Integer Integer.MAX_VALUE throw new NumberFormatException(); new NumberFormatException() return (int) nl; (int) nl public double nextDouble() {
        return Double.parseDouble(next());
    } nextDouble {
        return Double.parseDouble(next());
    } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public class Main {
    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        String a = sc.next();
        String b = sc.next();
        String c = sc.next();
        char[] ca = a.toCharArray();
        char[] cb = b.toCharArray();
        char[] cc = c.toCharArray();
        int pos = 0;
        int i = 0;
        int j = 0;
        int k = 0;
        while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        }
    }
} public class Main {
    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        String a = sc.next();
        String b = sc.next();
        String c = sc.next();
        char[] ca = a.toCharArray();
        char[] cb = b.toCharArray();
        char[] cc = c.toCharArray();
        int pos = 0;
        int i = 0;
        int j = 0;
        int k = 0;
        while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        }
    }
} Main
import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) {
        FastScanner sc = new FastScanner();
        String a = sc.next();
        String b = sc.next();
        String c = sc.next();
        char[] ca = a.toCharArray();
        char[] cb = b.toCharArray();
        char[] cc = c.toCharArray();
        int pos = 0;
        int i = 0;
        int j = 0;
        int k = 0;
        while (true) {
            if (pos == 0) {
                if (i >= a.length()) {
                    System.out.println("A");
                    return;
                }
                if (ca[i] == 'a') {
                    pos = 0;
                } else if (ca[i] == 'b') {
                    pos = 1;
                } else if (ca[i] == 'c') {
                    pos = 2;
                }
                i++;
            } else if (pos == 1) {
                if (j >= b.length()) {
                    System.out.println("B");
                    return;
                }
                if (cb[j] == 'a') {
                    pos = 0;
                } else if (cb[j] == 'b') {
                    pos = 1;
                } else if (cb[j] == 'c') {
                    pos = 2;
                }
                j++;
            } else {
                if (k >= c.length()) {
                    System.out.println("C");
                    return;
                }
                if (cc[k] == 'a') {
                    pos = 0;
                } else if (cc[k] == 'b') {
                    pos = 1;
                } else if (cc[k] == 'c') {
                    pos = 2;
                }
                k++;
            }
        }
    }
}

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        } else {
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() {
        if (hasNextByte())
            return buffer[ptr++];
        else
            return -1;
    }

    private static boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr]))
            ptr++;
        return hasNextByte();
    }

    public String next() {
        if (!hasNext())
            throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public long nextLong() {
        if (!hasNext())
            throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while (true) {
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            } else if (b == -1 || !isPrintableChar(b)) {
                return minus ? -n : n;
            } else {
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }

    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
            throw new NumberFormatException();
        return (int) nl;
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }
}
