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;
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
int i, j;
long long int ceil_div(long long int x, long long int y) {
  return (x + y - 1) / y;
}
int fast_pow(int a, int p) {
  int res = 1;
  while (p) {
    if (p % 2 == 0) {
      a = a * 1ll * a % 1000000007;
      p /= 2;
    } else {
      res = res * 1ll * a % 1000000007;
      p--;
    }
  }
  return res;
}
void test_cases() {
  string second;
  cin >> second;
  second.push_back('b');
  int n = second.length();
  vector<int> a;
  int na = 0;
  int count = 0;
  for (i = 0; i < n; i++) {
    if (second[i] == 'a') {
      count++;
    }
    if (second[i] == 'b') {
      na += count;
      if (count > 0) {
        a.push_back(count);
      }
      count = 0;
    }
  }
  int ans = 1;
  if (a.size() > 1) {
    for (auto x : a) {
      ans *= ((x + 1)) % 1000000007;
      ans = ans % 1000000007;
    }
    cout << ans - 1 << "\n";
  } else {
    cout << na << "\n";
  }
  return;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int T = 1;
  while (T--) {
    test_cases();
  }
  return 0;
}
