#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
template <typename T, typename TT>
inline ostream &operator<<(ostream &os, const pair<T, TT> &t) {
  return os << t.first << " " << t.second;
}
template <typename T>
inline ostream &operator<<(ostream &os, const vector<T> &t) {
  for (auto i : t) os << i << " ";
  return os;
}
template <typename T>
inline istream &operator>>(istream &is, vector<T> &v) {
  for (T &t : v) is >> t;
  return is;
}
template <typename T1, typename T2>
inline istream &operator>>(istream &is, pair<T1, T2> &t) {
  is >> t.first >> t.second;
  return is;
}
const long long mod = 1e9 + 7;
void solve() {
  string s;
  cin >> s;
  long long n = s.size();
  vector<long long> dp(n + 1);
  long long ls = 0;
  for (int i = 1; i <= n; i++) {
    dp[i] = dp[i - 1];
    if (s[i - 1] == 'a')
      (dp[i] += dp[ls] + 1) %= mod;
    else if (s[i - 1] == 'b')
      ls = i;
  }
  cout << dp[n] << '\n';
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  ;
  int T = 1;
  while (T--) {
    solve();
  }
  return 0;
}
