import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		
		Scanner sc = new Scanner(System.in);
		char [] a = sc.next().toCharArray();
		char [] b = sc.next().toCharArray();
		char [] c = sc.next().toCharArray();
		char turn = 'a';
		int an = 0;
		int bn = 0;
		int cn = 0;
		
		
		roop : while(true){
		switch(turn){
		case 'a' : if(a.length == an){System.out.println("A"); break roop;} 
		           turn = a[an]; an += 1; break;
		case 'b' : if(b.length == bn){System.out.println("B"); break roop;} 
				   turn = b[bn]; bn += 1; break;
		case 'c' : if(c.length == cn){System.out.println("C"); break roop;} 
				   turn = c[cn]; cn += 1; break;
		default :}}
	}} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args){
		
		Scanner sc = new Scanner(System.in);
		char [] a = sc.next().toCharArray();
		char [] b = sc.next().toCharArray();
		char [] c = sc.next().toCharArray();
		char turn = 'a';
		int an = 0;
		int bn = 0;
		int cn = 0;
		
		
		roop : while(true){
		switch(turn){
		case 'a' : if(a.length == an){System.out.println("A"); break roop;} 
		           turn = a[an]; an += 1; break;
		case 'b' : if(b.length == bn){System.out.println("B"); break roop;} 
				   turn = b[bn]; bn += 1; break;
		case 'c' : if(c.length == cn){System.out.println("C"); break roop;} 
				   turn = c[cn]; cn += 1; break;
		default :}}
	}} Main public static void main(String[] args){
		
		Scanner sc = new Scanner(System.in);
		char [] a = sc.next().toCharArray();
		char [] b = sc.next().toCharArray();
		char [] c = sc.next().toCharArray();
		char turn = 'a';
		int an = 0;
		int bn = 0;
		int cn = 0;
		
		
		roop : while(true){
		switch(turn){
		case 'a' : if(a.length == an){System.out.println("A"); break roop;} 
		           turn = a[an]; an += 1; break;
		case 'b' : if(b.length == bn){System.out.println("B"); break roop;} 
				   turn = b[bn]; bn += 1; break;
		case 'c' : if(c.length == cn){System.out.println("C"); break roop;} 
				   turn = c[cn]; cn += 1; break;
		default :}}
	} main {
		
		Scanner sc = new Scanner(System.in);
		char [] a = sc.next().toCharArray();
		char [] b = sc.next().toCharArray();
		char [] c = sc.next().toCharArray();
		char turn = 'a';
		int an = 0;
		int bn = 0;
		int cn = 0;
		
		
		roop : while(true){
		switch(turn){
		case 'a' : if(a.length == an){System.out.println("A"); break roop;} 
		           turn = a[an]; an += 1; break;
		case 'b' : if(b.length == bn){System.out.println("B"); break roop;} 
				   turn = b[bn]; bn += 1; break;
		case 'c' : if(c.length == cn){System.out.println("C"); break roop;} 
				   turn = c[cn]; cn += 1; break;
		default :}}
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) char [] a = sc.next().toCharArray(); a sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc char [] b = sc.next().toCharArray(); b sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc char [] c = sc.next().toCharArray(); c sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc char turn = 'a'; turn 'a' int an = 0; an 0 int bn = 0; bn 0 int cn = 0; cn 0 String[] args args public class Main {
	public static void main(String[] args){
		
		Scanner sc = new Scanner(System.in);
		char [] a = sc.next().toCharArray();
		char [] b = sc.next().toCharArray();
		char [] c = sc.next().toCharArray();
		char turn = 'a';
		int an = 0;
		int bn = 0;
		int cn = 0;
		
		
		roop : while(true){
		switch(turn){
		case 'a' : if(a.length == an){System.out.println("A"); break roop;} 
		           turn = a[an]; an += 1; break;
		case 'b' : if(b.length == bn){System.out.println("B"); break roop;} 
				   turn = b[bn]; bn += 1; break;
		case 'c' : if(c.length == cn){System.out.println("C"); break roop;} 
				   turn = c[cn]; cn += 1; break;
		default :}}
	}} public class Main {
	public static void main(String[] args){
		
		Scanner sc = new Scanner(System.in);
		char [] a = sc.next().toCharArray();
		char [] b = sc.next().toCharArray();
		char [] c = sc.next().toCharArray();
		char turn = 'a';
		int an = 0;
		int bn = 0;
		int cn = 0;
		
		
		roop : while(true){
		switch(turn){
		case 'a' : if(a.length == an){System.out.println("A"); break roop;} 
		           turn = a[an]; an += 1; break;
		case 'b' : if(b.length == bn){System.out.println("B"); break roop;} 
				   turn = b[bn]; bn += 1; break;
		case 'c' : if(c.length == cn){System.out.println("C"); break roop;} 
				   turn = c[cn]; cn += 1; break;
		default :}}
	}} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		
		Scanner sc = new Scanner(System.in);
		char [] a = sc.next().toCharArray();
		char [] b = sc.next().toCharArray();
		char [] c = sc.next().toCharArray();
		char turn = 'a';
		int an = 0;
		int bn = 0;
		int cn = 0;
		
		
		roop : while(true){
		switch(turn){
		case 'a' : if(a.length == an){System.out.println("A"); break roop;} 
		           turn = a[an]; an += 1; break;
		case 'b' : if(b.length == bn){System.out.println("B"); break roop;} 
				   turn = b[bn]; bn += 1; break;
		case 'c' : if(c.length == cn){System.out.println("C"); break roop;} 
				   turn = c[cn]; cn += 1; break;
		default :}}
	}}