#include<stdio.h>
int main() {
	int mur[4] = { 0 }; 
    int i;
	for (i = 0; i < 4; i++) 
	{
		mur[i] = 1; 
		if ((mur[0] != 1) +(mur[2] == 1) +(mur[3] == 1) +(mur[3] != 1) == 3){
			break; 
		}
		mur[i] = 0;
	}
	printf("%c",'A'+i);
	return 0;
}