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;
inline long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
inline long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
int month[15] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int dir[8][2] = {{-1, 0},  {1, 0}, {0, -1}, {0, 1},
                 {-1, -1}, {1, 1}, {1, -1}, {-1, 1}};
const int MAXN = 1e5 + 5;
const int INF = 1 << 30;
const long long mod = 1e9 + 7;
const double eps = 1e-8;
const long long inff = 0x3f3f3f3f3f3f3f3f;
int main() {
  string s;
  cin >> s;
  long long dp[MAXN], l = s.length() - 1, a[MAXN], cnt = 1, ans = 1;
  for (int i = 0; i <= l; i++) {
    if (s[i] == 'a')
      a[cnt]++;
    else if (s[i] == 'b' && a[cnt] != 0)
      cnt++;
  }
  if (cnt == 1) {
    cout << a[cnt] << endl;
    return 0;
  }
  for (int i = 1; i <= cnt; i++) ans = (ans * (a[i] + 1)) % mod;
  ans--;
  cout << ans << endl;
}
