import java.io.*;
import java.util.*;
public class Main {
	
	public static void main(String[] args) {
	
		MyScanner sc = new MyScanner();
		String s_a=sc.next();
		String s_b=sc.next();
		String s_c=sc.next();
		int la=s_a.length();
		int lb=s_b.length();
		int lc=s_c.length();
		int a=la;
		int b=lb;
		int c=lc;
		char turn='a';
		String ans=null;
		boolean end=false;
		while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		}
		
	
		System.out.println(ans);
	}
	
	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

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

		long nextLong() {
			return Long.parseLong(next());
		}

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

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}
	

}


 import java.io.*; io.* java import java.util.*; util.* java public class Main {
	
	public static void main(String[] args) {
	
		MyScanner sc = new MyScanner();
		String s_a=sc.next();
		String s_b=sc.next();
		String s_c=sc.next();
		int la=s_a.length();
		int lb=s_b.length();
		int lc=s_c.length();
		int a=la;
		int b=lb;
		int c=lc;
		char turn='a';
		String ans=null;
		boolean end=false;
		while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		}
		
	
		System.out.println(ans);
	}
	
	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

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

		long nextLong() {
			return Long.parseLong(next());
		}

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

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}
	

} Main public static PrintWriter out; out public static void main(String[] args) {
	
		MyScanner sc = new MyScanner();
		String s_a=sc.next();
		String s_b=sc.next();
		String s_c=sc.next();
		int la=s_a.length();
		int lb=s_b.length();
		int lc=s_c.length();
		int a=la;
		int b=lb;
		int c=lc;
		char turn='a';
		String ans=null;
		boolean end=false;
		while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		}
		
	
		System.out.println(ans);
	} main {
	
		MyScanner sc = new MyScanner();
		String s_a=sc.next();
		String s_b=sc.next();
		String s_c=sc.next();
		int la=s_a.length();
		int lb=s_b.length();
		int lc=s_c.length();
		int a=la;
		int b=lb;
		int c=lc;
		char turn='a';
		String ans=null;
		boolean end=false;
		while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		}
		
	
		System.out.println(ans);
	} MyScanner sc = new MyScanner(); sc new MyScanner() String s_a=sc.next(); s_a sc.next() sc.next sc String s_b=sc.next(); s_b sc.next() sc.next sc String s_c=sc.next(); s_c sc.next() sc.next sc int la=s_a.length(); la s_a.length() s_a.length s_a int lb=s_b.length(); lb s_b.length() s_b.length s_b int lc=s_c.length(); lc s_c.length() s_c.length s_c int a=la; a la int b=lb; b lb int c=lc; c lc char turn='a'; turn 'a' String ans=null; ans null boolean end=false; end false while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		} !end end {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		} switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			} turn case('a'): ('a') case('a'): if(a==0) {
					end=true;
					ans="A";
					break;
				} a==0 a 0 {
					end=true;
					ans="A";
					break;
				} end=true end true ans="A" ans "A" break; turn=s_a.charAt(la-a) turn s_a.charAt(la-a) s_a.charAt s_a la-a la a a-- a break; case('b'): ('b') case('b'): if(b==0) {
					end=true;
					ans="B";
					break;
				} b==0 b 0 {
					end=true;
					ans="B";
					break;
				} end=true end true ans="B" ans "B" break; turn=s_b.charAt(lb-b) turn s_b.charAt(lb-b) s_b.charAt s_b lb-b lb b b-- b break; case('c'): ('c') case('c'): if(c==0) {
					end=true;
					ans="C";
					break;
				} c==0 c 0 {
					end=true;
					ans="C";
					break;
				} end=true end true ans="C" ans "C" break; turn=s_c.charAt(lc-c) turn s_c.charAt(lc-c) s_c.charAt s_c lc-c lc c c-- c break; System.out.println(ans) System.out.println System.out System System.out ans String[] args args public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

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

		long nextLong() {
			return Long.parseLong(next());
		}

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

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	} MyScanner BufferedReader br; br StringTokenizer st; st public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		} MyScanner {
			br = new BufferedReader(new InputStreamReader(System.in));
		} br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		} next {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		} while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			} st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			} try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				} catch (IOException e) {
					e.printStackTrace();
				} IOException e {
					e.printStackTrace();
				} e.printStackTrace() e.printStackTrace e {
					st = new StringTokenizer(br.readLine());
				} st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {
			return Integer.parseInt(next());
		} nextInt {
			return Integer.parseInt(next());
		} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {
			return Long.parseLong(next());
		} nextLong {
			return Long.parseLong(next());
		} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
			return Double.parseDouble(next());
		} nextDouble {
			return Double.parseDouble(next());
		} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		} nextLine {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		} String str = ""; str "" try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			} IOException e {
				e.printStackTrace();
			} e.printStackTrace() e.printStackTrace e {
				str = br.readLine();
			} str = br.readLine() str br.readLine() br.readLine br return str; str public class Main {
	
	public static void main(String[] args) {
	
		MyScanner sc = new MyScanner();
		String s_a=sc.next();
		String s_b=sc.next();
		String s_c=sc.next();
		int la=s_a.length();
		int lb=s_b.length();
		int lc=s_c.length();
		int a=la;
		int b=lb;
		int c=lc;
		char turn='a';
		String ans=null;
		boolean end=false;
		while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		}
		
	
		System.out.println(ans);
	}
	
	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

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

		long nextLong() {
			return Long.parseLong(next());
		}

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

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}
	

} public class Main {
	
	public static void main(String[] args) {
	
		MyScanner sc = new MyScanner();
		String s_a=sc.next();
		String s_b=sc.next();
		String s_c=sc.next();
		int la=s_a.length();
		int lb=s_b.length();
		int lc=s_c.length();
		int a=la;
		int b=lb;
		int c=lc;
		char turn='a';
		String ans=null;
		boolean end=false;
		while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		}
		
	
		System.out.println(ans);
	}
	
	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

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

		long nextLong() {
			return Long.parseLong(next());
		}

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

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}
	

} Main
import java.io.*;
import java.util.*;
public class Main {
	
	public static void main(String[] args) {
	
		MyScanner sc = new MyScanner();
		String s_a=sc.next();
		String s_b=sc.next();
		String s_c=sc.next();
		int la=s_a.length();
		int lb=s_b.length();
		int lc=s_c.length();
		int a=la;
		int b=lb;
		int c=lc;
		char turn='a';
		String ans=null;
		boolean end=false;
		while(!end) {
			switch(turn) {
			case('a'):
				if(a==0) {
					end=true;
					ans="A";
					break;
				}
				turn=s_a.charAt(la-a);
				a--;
				
				break;
				
				
			case('b'):
				if(b==0) {
					end=true;
					ans="B";
					break;
				}
				turn=s_b.charAt(lb-b);
				b--;
				
				break;
			
			case('c'):
				if(c==0) {
					end=true;
					ans="C";
					break;
				}
				turn=s_c.charAt(lc-c);
				c--;
		
				break;
			}
		}
		
	
		System.out.println(ans);
	}
	
	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

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

		long nextLong() {
			return Long.parseLong(next());
		}

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

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}
	

}



