import java.util.Scanner;


public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] s = new String[3];
		for (int i = 0; i < 3; i++) {
			s[i] = sc.next();
		}
		int i = 0;

		while (s[i].length()!=0) {
			int n = s[i].charAt(0) - 'a';
			s[i] = s[i].substring(1);
			i=n;
		}
		System.out.println((char)('A'+i));

	}

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz