http://codeforces.com/contest/550/problem/A

#include <iostream>
#include <string>

using namespace std;

int main(){
    string  a;
    cin>>a;

    bool isAns=false;

    int k=a.length();
    for(int i=0;i<a.length()-1;i++){
        if(a[i]=='A' && a[i+1]=='B'){
            k=i+2;
            break;
        }
    }
    for(int i=k; i<a.length()-1;i++){
        if(a[i]=='B' && a[i+1]=='A'){
            cout<<"YES";
            return 0;
        }
    }
    k=a.length();

    for(int i=0;i<a.length()-1;i++){
        if(a[i]=='B' && a[i+1]=='A'){
            k=i+2;
            break;
        }
    }
    for(int i=k; i<a.length()-1;i++){
        if(a[i]=='A' && a[i+1]=='B'){
            cout<<"YES";
            return 0;
        }
    }

    cout<<"NO";
}