#include <bits/stdc++.h>
const long long int mod = 1e9 + 7;
using namespace std;
int main() {
  ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
  string s;
  cin >> s;
  int n = int((s).size());
  s = "#" + s;
  long long int seq = 0, seq1 = 0;
  for (long long int i = (1); i <= (n); i++) {
    if (s[i] == 'a')
      seq += seq1 + 1;
    else if (s[i] == 'b')
      seq1 = seq;
    seq = seq % mod;
  }
  cout << seq << endl;
}
