aaaaabb
 aabaaaa
 babbabaabbbbabwbvbhbbbaaabbabbbbbbbkabbbbabaaabbbbbbajabbaaabazbbbzbalbabbwbbaabbabacabdbabbbfaaabbb
 baaahbbbba
 ababavvvv
 abnxabbaab
 krflnzhter
 amaabbbbxaabbbabaabaabbaaabaaaaabibbabaabaaabaabcaaxabablbbbbmbbbaaaaaabbaabbbaaabaaaababaababbabbbb
 babbbaaaaaabbbaabaaaaaoaabababaababaaaaababaaaaaaabbbbbbaaapaabaaabaaababaaaabaaaabaaaaababaaaabaaab

5
 14
 42467327
 7
 7
 11
 0
 98718509
 813881762

#include <bits/stdc++.h>
long long power(long long a, long long b, long long m) {
  if (b == 0) return 1;
  if (b == 1) return a % m;
  long long t = power(a, b / 2, m);
  t = (t * t) % m;
  if (b & 1) t = (t * a) % m;
  return t;
}
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  string second;
  cin >> second;
  long long n = second.length();
  vector<long long> v;
  long long a = 0, b = 0;
  long long i = 0;
  while (i < n) {
    while (i < n && second[i] != 'b') {
      if (second[i] == 'a') a++;
      i++;
    }
    if (a) v.push_back(a);
    a = 0;
    while (i < n && second[i] != 'a') {
      i++;
    }
  }
  long long ans = 1;
  for (long long i = 0; i < v.size(); i++) {
    ans = (ans * (v[i] + 1)) % 1000000007;
  }
  ans--;
  ans += 1000000007;
  ans %= 1000000007;
  cout << ans;
}
