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();
  long long b = 0, k = 0, a = 0;
  long long ans = -1;
  for (long long i = 0; i < n; i++) {
    if (second[i] == 'a') a++;
    if (second[i] == 'b') b++;
  }
  if (b == 0 || a == 0) {
    cout << a;
    return 0;
  }
  b = 0;
  for (long long i = 0; i < n; i++) {
    if (second[i] == 'a') {
      if (k == 0) {
        k++;
      } else if (b) {
        k++;
      } else {
        ans++;
      }
      b = 0;
    } else if (second[i] == 'b') {
      b++;
    }
  }
  if (ans == -1) ans = 0;
  ans += power(2, k, 1000000007);
  cout << ans;
}
