#include<iostream>
using namespace std;

void swap(int* x, int* y)
{
	int *z = x;
	x = y;
	y = z;
}

int main()
{
	int a[3] = {1,0,0};
	char x, y;
	char d;

	while (cin >> x >> d >> y){
		swap(&a[x-'A'+1],&a[y-'A'+1]);
	}

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

	return 0;
}