#include <bits/stdc++.h>
using namespace std;
long long powr(long long exp) {
  if (exp == 1) return 2;
  if (exp % 2 == 0) {
    long long ret = (powr(exp / 2)) % 1000000007;
    ret = (ret * ret) % 1000000007;
    return ret;
  }
  long long ret = powr(exp / 2) % 1000000007;
  ret = (ret * ret * 2) % 1000000007;
  return ret;
}
int main() {
  string s;
  cin >> s;
  long long mul = 1;
  string s1 = "";
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == 'a' || s[i] == 'b') s1 += s[i];
  }
  s1 += 'b';
  long long st = 1;
  for (int i = 0; i < s1.size(); i++) {
    if (s1[i] == 'b') {
      mul = ((mul) * (st % 1000000007)) % 1000000007;
      st = 1;
    } else if (s1[i] == 'a') {
      st++;
    }
  }
  mul = (mul - 1);
  if (mul < 0) mul += 1000000007;
  cout << mul;
}
