#include <stdio.h>

char stack[100];
int top = -1;

void push(char x) {
    stack[++top] = x;
}

void pop() {
    top--;
}

int main() {
    char input[] = {'A','A','B','A','B','B'};
    int n = sizeof(input) / sizeof(input[0]);

    for (int i = 0; i < n; i++) {
        push(input[i]);

        if (top >= 1 && stack[top-1] == 'A' && stack[top] == 'B') {
            pop();
            pop();
        }
    }

    for (int j = 0; j <= top; j++) {
        printf("%c ", stack[j]);
    }

    return 0;
}