#include <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>

using namespace std;
typedef long long ll;

int main(void) {
    int N;
    cin >> N;
    if (N % 3 == 1) cout << "B" << endl;
    else cout << "A" << endl;
    return 0;
}