func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MOD = 1e9 + 7;   int main() {     string s;     cin >> s;     int k = 0, c = 0;     for (int i = s.size() - 1; i >= 0; i--) {       if (s[i] ==  b )         c++;       else {         k += c;         c *= 2;         k %= MOD;         c %= MOD;       }     }     cout << k <<   n ;     return 0;   }   