import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.List;
import java.util.Arrays;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.List; List java.util import java.util.Arrays; Arrays java.util import java.util.StringTokenizer; StringTokenizer java.util import java.io.IOException; IOException java.io import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.ArrayList; ArrayList java.util import java.io.InputStream; InputStream java.io public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out InputReader in = new InputReader(inputStream); in new InputReader(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) TaskB solver = new TaskB(); solver new TaskB() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        }

    } TaskB public void solve(int testNumber, InputReader in, PrintWriter out) {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        } solve {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        } char[] A = in.next().toCharArray(); A in.next().toCharArray() in.next().toCharArray in.next() in.next in char[] B = in.next().toCharArray(); B in.next().toCharArray() in.next().toCharArray in.next() in.next in char[] C = in.next().toCharArray(); C in.next().toCharArray() in.next().toCharArray in.next() in.next in List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C)); players new ArrayList<>(Arrays.asList(A, B, C)) int[] points = {A.length, B.length, C.length}; points {A.length, B.length, C.length} A.length A A.length B.length B B.length C.length C C.length int[] index = {0, 0, 0}; index {0, 0, 0} 0 0 0 char[] winner = {'A', 'B', 'C'}; winner {'A', 'B', 'C'} 'A' 'B' 'C' int cur = 0; cur 0 while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            } true {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            } if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                } points[cur] == 0 points[cur] points cur 0 {
                    out.println(winner[cur]);
                    break;
                } out.println(winner[cur]) out.println out winner[cur] winner cur break; --points[cur] points[cur] points cur ++index[cur] index[cur] index cur cur = players.get(cur)[index[cur] - 1] - 'a' cur players.get(cur)[index[cur] - 1] - 'a' players.get(cur)[index[cur] - 1] players.get(cur) players.get players cur index[cur] - 1 index[cur] index cur 1 'a' int testNumber testNumber InputReader in in PrintWriter out out static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    } InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(stream), 32768) reader new BufferedReader(new InputStreamReader(stream), 32768) tokenizer = null tokenizer null InputStream stream stream public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    tokenizer = new StringTokenizer(reader.readLine());
                } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.List;
import java.util.Arrays;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            char[] A = in.next().toCharArray();
            char[] B = in.next().toCharArray();
            char[] C = in.next().toCharArray();

            List<char[]> players = new ArrayList<>(Arrays.asList(A, B, C));
            int[] points = {A.length, B.length, C.length};
            int[] index = {0, 0, 0};
            char[] winner = {'A', 'B', 'C'};

            int cur = 0;
            while (true) {
                if (points[cur] == 0) {
                    out.println(winner[cur]);
                    break;
                }
                --points[cur];
                ++index[cur];
                cur = players.get(cur)[index[cur] - 1] - 'a';

            }
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

    }
}

