#include <iostream>

using namespace std;

int main() {
    char x, y, answer;
    cin >> x >> y >> answer;

    if(answer == 'D') {
        cout << y << endl;
    }
    else {
        for(char c = 'A'; c <= 'C'; c++) {
            if(c != x and c != y) {
                cout << c << endl;
                break;
            }
        }
    }


    return 0;
}