#include <bits/stdc++.h>
using namespace std;
int gcd1(int a, int b) {
  if (a == 0) return b;
  return gcd1(b % a, a);
}
long long modx(long long base, long long ex) {
  long long ans = 1LL, val = base;
  while (ex > 0LL) {
    if (ex & 1LL) ans = (ans * val) % 1000000007;
    val = (val * val) % 1000000007;
    ex = ex >> 1LL;
  }
  return ans;
}
string s;
int lb[300005];
long long ans[300005], sum[300005];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> s;
  int n = s.length();
  int pa = -1, push_back = -1;
  for (int i = 0; i < n; i++) {
    if (s[i] == 'a') {
      lb[i] = push_back;
    } else if (s[i] == 'b')
      push_back = i;
  }
  if (s[0] == 'a') ans[0] = 1;
  sum[0] = ans[0];
  for (int i = 1; i < n; i++) {
    if (s[i] != 'a')
      ans[i] = 0;
    else {
      ans[i] = 1;
      if (lb[i] != -1) ans[i] = (ans[i] + sum[lb[i]]) % 1000000007;
    }
    sum[i] = (sum[i - 1] + ans[i]) % 1000000007;
  }
  cout << sum[n - 1] << endl;
  return 0;
}
