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

int main(){
    char str[13];
    int i, len, state = 0, cnt = 0, cnt_B = 0;

    scanf("%s", str);
    len = strlen(str);
    for(i = 0; i < len; i++){
        if(state == 0){
            if(str[i] == 'B'){
                state = 1;
                cnt_B++;
                continue;
            }
        }else if(state == 1){
            if(str[i] == 'A'){
                cnt += cnt_B;
                cnt_B = 1;
                continue;
            }else if(str[i] == 'B'){
                cnt_B++;
            }
        }
    }
    printf("%d\n", cnt);

    return 0;
}