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;
template <typename T>
inline void printV(vector<T>& a) {
  for (int i = 0; i < ((int)((a).size())); i++) {
    cout << a[i] << " ";
  }
  cout << "\n";
}
template <typename T>
inline void printV(vector<T>& a, int n) {
  for (int i = 0; i < n; i++) {
    cout << a[i] << " ";
  }
  cout << "\n";
}
template <typename T>
inline void printVV(vector<vector<T>>& a) {
  for (int i = 0; i < ((int)((a).size())); i++) {
    printV(a[i]);
  }
  cout << "\n";
}
template <typename T>
inline void clearVV(vector<vector<T>>& a) {
  for (auto& x : a) {
    x.clear();
  }
  a.clear();
}
template <typename T>
inline void assignVV(vector<vector<T>>& a, T val) {
  for (int i = 0; i < ((int)((a).size())); i++) {
    for (int j = 0; j < ((int)((a[i]).size())); j++) {
      a[i][j] = val;
    }
  }
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const long double eps = LDBL_EPSILON;
const int inf = 5e8;
const int modn = 1e9 + 7;
const int MAX = 1e5;
inline int add(int a, int b) {
  int ret = ((long long)a + b) % modn;
  if (ret < 0) {
    ret = (ret + modn) % modn;
  }
  return ret;
}
inline int mul(int a, int b) {
  int ret = ((long long)a * b) % modn;
  if (ret < 0) {
    ret = (ret + modn) % modn;
  }
  return ret;
}
inline int add(int a, int b, int c) {
  int ret = ((long long)a + b + c) % modn;
  if (ret < 0) {
    ret = (ret + modn) % modn;
  }
  return ret;
}
inline int mul(int a, int b, int c) {
  int ret = ((long long)a * b) % modn;
  return mul(ret, c);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  string s;
  cin >> s;
  vector<int> a;
  int cnt = 0;
  for (int i = 0; i < ((int)((s).size())); i++) {
    if (s[i] == 'a') {
      cnt++;
    }
    if (s[i] == 'b') {
      if (cnt != 0) {
        a.push_back(cnt);
        cnt = 0;
      }
    }
  }
  a.push_back(cnt);
  int n = a.size();
  function<int(int)> solve = [&](int i) {
    if (i == n - 1) {
      return a[i];
    }
    int nextval = solve(i + 1);
    return add(a[i], nextval, mul(a[i], nextval));
  };
  int ans = solve(0);
  cout << ans << "\n";
  return 0;
}
