#include <bits/stdc++.h>
using namespace std;
const int N = 1e9 + 7;
int main() {
  string s;
  cin >> s;
  int ans = 0;
  int t = 0;
  for (int i = s.length() - 1; i >= 0; i--) {
    if (s[i] == 'b')
      t = (t + 1) % N;
    else {
      ans = (ans + t) % N;
      t = (t * 2) % N;
    }
  }
  cout << ans << endl;
  return 0;
}
