#include<iostream>
using namespace std;

int main()
{
	int a[4] = { 1, 0, 0, -1 };
	char x, y;
	char d;

	while (cin >> x >> d >> y){
		auto swap = [](int* x, int* y){
			int* z = x;
			x = y;
			y = z;
		};

		auto getNum = [x, y](char z){
			switch (z){
			case 'A':	return 0;
			case 'B':	return 1;
			case 'C':	return 2;
			}				return 3;

		};

		swap(&a[getNum(x)], &a[getNum(y)]);
	}


	for (int i = 0; i < 3; ++i)
	if (a[i] == 1)
		cout << static_cast<char>('A' + i) << endl;

	return 0;
}