#include <iostream>
using namespace std;
int main()
{
    char c[5];
    char n[] = "A";
    while(cin>>c){
        if(c[0]==n[0]) n[0] = c[2];
        else if( c[2] == n[0] ) n[0] = c[0];
    }
    putchar(n[0]);
    putcharendl);
    return 0;
}