#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  bool res = false;
  for (int i = 0; i < s.size() - 1; ++i) {
    if (s[i] == 'A' && s[i + 1] == 'B') {
      for (int j = i + 2; j < s.size() - 1; ++j) {
        if (s[j] == 'B' && s[j + 1] == 'A') {
          cout << "YES\n";
          return 0;
        }
      }
      break;
    }
  }
  for (int i = 0; i < s.size() - 1; ++i) {
    if (s[i] == 'B' && s[i + 1] == 'A') {
      for (int j = i + 2; j < s.size() - 1; ++j) {
        if (s[j] == 'A' && s[j + 1] == 'B') {
          cout << "YES\n";
          return 0;
        }
      }
      break;
    }
  }
  cout << "NO\n";
  return 0;
}
