/*
TASK: gen
LANG: C++
*/

#include <iostream>
#include <string>
using namespace std;

int main()
{
	string a;
	cin >> a;
	
	int n;
	cin >> n;
	for ( int i = 0 ; i < n ; i++ )
		cin >> a;
	cin >> n;
	for ( int i = 0 ; i < n ; i++ )
		cin >> a;

	if ( n == 4 ) cout << "BC";
	else cout << "AB" << endl;
}
