#include <bits/stdc++.h>
using namespace std;

int n, m, k;

int gcd(int x, int y) {
	if (x < y) swap(x, y);
	if (y == 0) return x;
	return gcd(y, x%y);
}

int main() {
	scanf("%d %d %d\n", &n, &m, &k);
	if ((n*m) % k != 0) {
		printf("impossible\n");
		return 0;
	}
	int area = (n*m)/k;
	int x = gcd(area, n);
	int y = area / x;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			printf("%c", 'A' + (m/y) * (i/x) + j/y);
		}
		printf("\n");
	}
}