#include <bits/stdc++.h>
using namespace std;
int main() {
  string a;
  cin >> a;
  long long int x = a.length();
  std::vector<long long int> v;
  long long int c = 0;
  long long int d = 0;
  for (long long int i = 0; i < x; i++) {
    if (a[i] == 'b') {
      d++;
    }
    if (a[i] == 'a') {
      if (d > 0 && c > 0) {
        v.push_back(c);
        d = 0;
        c = 0;
      }
      c++;
      d = 0;
    }
  }
  if (c > 0) v.push_back(c);
  long long int res = 1;
  for (long long int i = 0; i < v.size(); i++) {
    res = (res * (v[i] + 1)) % 1000000007;
  }
  cout << res - 1;
  return 0;
}
