【Codeforces】550A-Two Substrings

//Author:Fczhao
//Language:cpp
#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false);
  string s; cin >> s;
  int n = s.length();
  int ab = 0, ba = 0, all = 0;
  for(int i = 0; i < n - 1; i++) {
    if(s.substr(i, 3) == "ABA") {
      all++;
      i += 2;
    }
    else if(s.substr(i, 3) == "BAB") {
      all++;
      i += 2;
    }
    else if(s.substr(i, 2) == "AB") {
      ab++;
      i++;
    }
    else if(s.substr(i, 2) == "BA") {
      ba++;
      i++;
    }
  }
  if(all >= 2) cout << "YES" << endl;
  else if(all >= 1 && (ab || ba)) cout << "YES" << endl;
  else if(ab && ba) cout << "YES" << endl;
  else cout << "NO" << endl;
  return 0;
}