import java.util.*;
public class Main{
static long comb(int n, int m, int k) {
long res = 1L;
for(int i=1; i <= m; i++) {
res = res*(n-m+i)/i;
if(res > k) break;
}
return res;
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt(), m = sc.nextInt(), k = sc.nextInt();
if(comb(m+n, m, k) < k) System.out.println(-1);
else {
char[] res = new char[m+n];
int idx = 0;
while(n != 0 && m != 0) {
long tmp = comb(n+m-1, m, k);
if(tmp < k) {
k -= tmp;
res[idx++] = 'z';
m --;
} else {
res[idx++] = 'a';
n --;
}
}
for(int i=0; i < n; i++) res[idx++] = 'a';
for(int j=0; j < m; j++) res[idx++] = 'z';
System.out.println(String.valueOf(res));
}
}
}