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

/**
 * 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);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();
	}

	static class Task {
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		}
	}
	
	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 int nextInt() {
			return Integer.parseInt(next());
		}

	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.OutputStream; OutputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.ArrayList; ArrayList java.util import java.util.List; List java.util import java.util.StringTokenizer; StringTokenizer java.util 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);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();
	}

	static class Task {
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		}
	}
	
	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 int nextInt() {
			return Integer.parseInt(next());
		}

	}
} 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);
		Task solver = new Task();
		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);
		Task solver = new Task();
		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) Task solver = new Task(); solver new Task() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class Task {
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		}
	} Task public void solve(int testNumber, InputReader in, PrintWriter out) {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		} solve {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		} String A = in.next(); A in.next() in.next in String B = in.next(); B in.next() in.next in String C = in.next(); C in.next() in.next in char turn = 'a'; turn 'a' int countA = 0; countA 0 int countB = 0; countB 0 int countC = 0; countC 0 while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			} true {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			} if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				} turn == 'a' turn 'a' {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				} if(countA == A.length()) {
						out.println('A');
						break;
					} countA == A.length() countA A.length() A.length A {
						out.println('A');
						break;
					} out.println('A') out.println out 'A' break; turn = A.charAt(countA) turn A.charAt(countA) A.charAt A countA countA++ countA if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				} turn == 'b' turn 'b' {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				} if(countB == B.length()) {
						out.println('B');
						break;
					} countB == B.length() countB B.length() B.length B {
						out.println('B');
						break;
					} out.println('B') out.println out 'B' break; turn = B.charAt(countB) turn B.charAt(countB) B.charAt B countB countB++ countB {
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				} if(countC == C.length()) {
						out.println('C');
						break;
					} countC == C.length() countC C.length() C.length C {
						out.println('C');
						break;
					} out.println('C') out.println out 'C' break; turn = C.charAt(countC) turn C.charAt(countC) C.charAt C countC countC++ countC 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();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

	} 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 int nextInt() {
			return Integer.parseInt(next());
		} nextInt {
			return Integer.parseInt(next());
		} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next 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);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();
	}

	static class Task {
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		}
	}
	
	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 int nextInt() {
			return Integer.parseInt(next());
		}

	}
} 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);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();
	}

	static class Task {
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		}
	}
	
	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 int nextInt() {
			return Integer.parseInt(next());
		}

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

/**
 * 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);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();
	}

	static class Task {
		public void solve(int testNumber, InputReader in, PrintWriter out) {
			String A = in.next();
			String B = in.next();
			String C = in.next();
			char turn = 'a';
			int countA = 0;
			int countB = 0;
			int countC = 0;
			while(true) {
				if(turn == 'a') {
					if(countA == A.length()) {
						out.println('A');
						break;
					}
					turn = A.charAt(countA);
					countA++;
				}else if(turn == 'b') {
					if(countB == B.length()) {
						out.println('B');
						break;
					}
					turn = B.charAt(countB);
					countB++;
				}else{
					if(countC == C.length()) {
						out.println('C');
						break;
					}
					turn = C.charAt(countC);
					countC++;
				}
			}
		}
	}
	
	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 int nextInt() {
			return Integer.parseInt(next());
		}

	}
}
