#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
std::pair<T, U> operator+(const std::pair<T, U>& l, const std::pair<T, U>& r) {
  return {l.first + r.first, l.second + r.second};
}
typedef void (*callback_function)(void);
const long long INF64 = 1e18;
const long long INF32 = 1e9;
const long long MOD = 1e9 + 7;
const long double PI = acos(-1.0L);
const long double EPS = static_cast<long double>(1e-9);
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie();
  {
    string s;
    cin >> s;
    long long cur = 0, res = 0, MOD = 1e9 + 7;
    for (long long i = (s.length() - 1); i >= (0); i--) {
      if (s[i] == 'b')
        cur = (cur + 1) % MOD;
      else
        res = (res + cur) % MOD, cur = (cur * 2) % MOD;
    }
    cout << res << endl;
  }
  return 0;
}
