#include <iostream>
using namespace std;

const int MOD = int(1e9) + 7;
long long cnt, ans;

int main(){
    cin >> s;
    for(int i = s.size() - 1; i >= 0; i--){
        if(s[i] == 'b')
            cnt++;
            cnt %= MOD;
        else
            ans += cnt;
            ans %= MOD;
            cnt *= 2;
            cnt %= MOD;
    }
    cout << ans;
}