aaaaabb
 aabaaaa
 babbabaabbbbabwbvbhbbbaaabbabbbbbbbkabbbbabaaabbbbbbajabbaaabazbbbzbalbabbwbbaabbabacabdbabbbfaaabbb
 baaahbbbba
 ababavvvv
 abnxabbaab
 krflnzhter
 amaabbbbxaabbbabaabaabbaaabaaaaabibbabaabaaabaabcaaxabablbbbbmbbbaaaaaabbaabbbaaabaaaababaababbabbbb
 babbbaaaaaabbbaabaaaaaoaabababaababaaaaababaaaaaaabbbbbbaaapaabaaabaaababaaaabaaaabaaaaababaaaabaaab

5
 14
 42467327
 7
 7
 11
 0
 98718509
 813881762

#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
const int MAX = 100005;
long long modexp(long long x, long long n) {
  if (n == 0) return 1LL;
  if (n % 2 == 0) {
    long long y = modexp(x, n / 2) % mod;
    return (y * y) % mod;
  }
  return (x * modexp(x, n - 1) % mod) % mod;
}
long long powr(long long x, long long n) {
  long long ans = 1;
  for (int i = 1; i <= n; i++) ans = ans * x;
  return ans;
}
int main() {
  string s;
  cin >> s;
  string aux;
  int flag = 0;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == 'a') {
      flag = 1;
      aux += s[i];
    } else if (s[i] == 'b' && flag == 1) {
      flag = 0;
      aux += s[i];
    }
  }
  long long ans = 1;
  for (int i = 0; i < aux.size(); i++) {
    if (aux[i] == 'b') continue;
    int cnt = 0;
    while (aux[i] == 'a') {
      i++;
      cnt++;
    }
    ans = (ans * (cnt + 1)) % mod;
  }
  ans = (ans - 1 + mod) % mod;
  printf("%lld\n", ans);
  return 0;
}
