#include <bits/stdc++.h>
using namespace std;
#define int long long 
const long long nmax = 1e6;
string s;
bool check = false, check1 = false;
main()
{
    cin >> s;
    for (int i = 0; i < s . size() - 1; ++i)
    {
        if (s[i] == 'A' and s[i + 1] == 'B')
        {
            check = true;
            i++;
        }
    }
    for (int i = 0; i < s . size() - 1; ++i)
    {
        if (s[i] == 'B' and s[i + 1] == 'A')
        {
            check1 = true;
            i++;
        }
    }
    cout << (check and check1 ? "YES" : "NO");
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main() {
string s;
cin >> s;
bool ok=false,ok2=false;
for (int i=0;i<s.length()-1;i++) {
if (!ok && s.substr(i,2)=="AB") {
ok=true;
i++;
} else if (!ok2 && s.substr(i,2)=="BA") {
ok2=true;
i++;
}
if (ok && ok2) {
cout<<"YES"<<endl;
return 0;
}
}
cout<<"NO"<<endl;
return 0;
}