func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int n, k;     while (scanf( %d %d , &n, &k) == 2) {       char s[1000005];       memset(s, 0, sizeof(s));       int t = 0;       if (n == 1 && k == 1)         printf( a n );       else if (k == 1)         printf( -1 n );       else if (n < k)         printf( -1 n );       else if (k == 2) {         int l = k - 2;         for (int i = 1; i <= n - l; i++) {           if (i & 1)             s[t++] =  a ;           else             s[t++] =  b ;         }         s[t] =   0 ;         printf( %s n , s);       } else if (k == 3) {         int l = k - 2;         for (int i = 1; i <= n - l; i++) {           if (i & 1)             s[t++] =  a ;           else             s[t++] =  b ;         }         for (int i = 1; i <= l; i++) {           s[t++] = char( b  + i);         }         s[t] =   0 ;         printf( %s n , s);       } else {         int l = k - 2;         for (int i = 1; i <= n - l; i++) {           if (i & 1)             s[t++] =  a ;           else             s[t++] =  b ;         }         for (int i = 1; i <= l; i++) {           s[t++] = char( b  + i);         }         s[t] =   0 ;         printf( %s n , s);       }     }     return 0;   }   