func_code_string: #include <bits/stdc++.h>   using namespace std;   long n, k;   long ans[1000010];   int main() {     cin >> n >> k;     if ((k > n) || ((k <= n) && (k == 1) && (n != 1))) {       cout <<  -1  << endl;       return 0;     }     if ((n == 1) && (k == 1)) {       cout <<  a  << endl;       return 0;     }     if (!(n & 1)) {       ans[1] = 97;       ans[2] = 98;       long c(96 + k);       for (long i = n; i >= n - (k - 2) + 1; --i) ans[i] = c--;       cout <<  ab ;       for (long i = 1; i <= ((n - k) / 2); ++i) cout <<  ab ;       if (k & 1) cout <<  a ;       for (long i = (n - (k - 2) + 1); i <= n; ++i) cout << char(ans[i]);       cout << endl;     } else {       ans[1] = 97;       ans[2] = 98;       long c(96 + k);       for (long i = n; i >= n - (k - 2) + 1; --i) ans[i] = c--;       cout <<  ab ;       for (long i = 1; i <= ((n - k) / 2); ++i) cout <<  ab ;       if (!(k & 1)) cout <<  a ;       for (long i = (n - (k - 2) + 1); i <= n; ++i) cout << char(ans[i]);       cout << endl;     }     return 0;   }   