import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws IOException {

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String a = br.readLine();
		String b = br.readLine();
		String c = br.readLine();
		String n = a;

		while (n.length() > 0) {
			if (n.equals(a)) {
				if (a.substring(0, 1).equals("a")) {
					a = a.substring(1);
					n = a;
				} else if (a.substring(0, 1).equals("b")) {
					a = a.substring(1);
					n = b;
				} else if (a.substring(0, 1).equals("c")) {
					a = a.substring(1);
					n = c;
				}
			} else if (n.equals(b)) {
				if (b.substring(0, 1).equals("a")) {
					b = b.substring(1);
					n = a;
				} else if (b.substring(0, 1).equals("b")) {
					b = b.substring(1);
					n = b;
				} else if (b.substring(0, 1).equals("c")) {
					b = b.substring(1);
					n = c;
				}
			} else if (n.equals(c)) {
				if (c.substring(0, 1).equals("a")) {
					c = c.substring(1);
					n = a;
				} else if (c.substring(0, 1).equals("b")) {
					c = c.substring(1);
					n = b;
				} else if (c.substring(0, 1).equals("c")) {
					c = c.substring(1);
					n = c;
				}
			}
		}
		if (n == a) {
			System.out.println("A");
		} else if (n == b) {
			System.out.println("B");
		} else if (n == c) {
			System.out.println("C");
		}
	}
}

/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