#include <bits/stdc++.h>
using namespace std;
char s[110000];
int k, f[110000], g[110000];
int main() {
  scanf("%s", s + 1);
  int n = strlen(s + 1);
  for (int i = 1; i <= n; i++) {
    if (s[i] == 'a')
      f[i] = (g[k] + 1) % 1000000007;
    else if (s[i] == 'b')
      k = i;
    g[i] = (g[i - 1] + f[i]) % 1000000007;
  }
  cout << g[n];
  return 0;
}
