#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
int main() {
  string s;
  cin >> s;
  int k = 0, c = 0;
  for (int i = s.size() - 1; i >= 0; i--) {
    if (s[i] == 'b')
      c++;
    else {
      k += c;
      c *= 2;
      k %= MOD;
      c %= MOD;
    }
  }
  cout << k << "\n";
  return 0;
}
