func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int n, k;     cin >> n >> k;     if (n < k || (n > 1 && k == 1)) {       cout << -1 << endl;       return 0;     }     if (n <= 2) {       n == 1 ? cout <<  a  << endl : cout <<  ab  << endl;       return 0;     }     char *str = new char[n + 1];     str[n] =   0 ;     int pos = 0;     int prev = 1;     char used =  a  - 1;     while (n - pos > k - 2) {       if (prev == 1) {         str[pos] =  a ;         prev = 0;       } else {         str[pos] =  b ;         prev = 1;       }       if (used < str[pos]) {         used = str[pos];       }       pos++;     }     while (pos != n) {       used++;       str[pos] = used;       pos++;     }     cout << str << endl;     return 0;   }   