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;
const int MOD = 1000000007;
const int N = 1000005;
const double PI = 4 * atan(1);
const long long MAX = 9223372036854775807;
int dx[] = {1, -1, 0, 0, 1, -1, 1, -1};
int dy[] = {0, 0, 1, -1, 1, 1, -1, -1};
long long gcd(long long a, long long b) { return (b == 0 ? a : gcd(b, a % b)); }
long long lcm(long long a, long long b) { return a * (b / gcd(a, b)); }
bool issquare(long long w) { return trunc(sqrt(w)) * trunc(sqrt(w)) == w; }
bool isprime(long long u) {
  for (long long i = 2; i <= (int)sqrt(u); i++) {
    if (u % i == 0) return 0;
  }
  return 1;
}
long long mod(long long to_mod, long long MOD) {
  to_mod %= MOD;
  while (to_mod < 0) to_mod += MOD;
  return to_mod % MOD;
}
long long moduloMultiplication(long long a, long long b) {
  long long res = 0;
  while (b) {
    if (b & 1) res = (res + a);
    a = (2 * a);
    b >>= 1;
  }
  return res;
}
long long power(long long x, long long y, long long p) {
  long long res = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1) res = (res * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return res;
}
long long q, y, k, z, w, t, l, r, x, n, m, ans, res;
string ch;
string sh;
vector<long long> v;
int main() {
  cin.tie(0);
  cout.tie(0);
  vector<long long> ccc;
  bool cond = false;
  cin >> ch;
  n = ch.size();
  sh = "";
  for (int i = 0; i < n; i++) {
    if (ch[i] == 'a' || ch[i] == 'b') {
      sh += ch[i];
      ccc.push_back(i);
    }
  }
  x = 0;
  n = sh.size();
  for (int i = 0; i < n; i++) {
    if (sh[i] == 'b') {
      if (x > 0) v.push_back(x);
      x = 0;
    }
    if (sh[i] == 'a') {
      x++;
      ccc.push_back(i);
    }
  }
  if (x > 0) v.push_back(x);
  if (v.size() == 0) {
    cout << 0;
    return 0;
  }
  res = 1;
  for (int i = 0; i < v.size(); i++) {
    ans += v[i] * res;
    res *= (v[i] + 1);
    res = mod(res, MOD);
    ans = mod(ans, MOD);
  }
  cout << ans;
  return 0;
}
