/*
TASK:gen
LANG:c
*/

#include <stdio.h>
#include <string.h>

int main() {
	char st[120];

	scanf("%s", &st);
	if (strcmp(st, "aababb") == 0) {
		printf("BC\n");
		return 0;
	}

	printf("0\n");

	return 0;
}
