#include <bits/stdc++.h>
using namespace std;
const int N = 20 + 1, INF = 0x3f3f3f3f;
int f[N][N][N], w, h, m;
void solve();
int main()
{
	while(scanf("%d%d%d", &w, &h, &m) != EOF){
		
		if(w == 0 && h == 0 && m == 0) break;
		solve();
		printf("%d\n", f[w][h][m]);
		
	}
	
	return 0;
}

void solve()
{
	memset(f, 0, sizeof(f));
	int i, j, k;
	int t, p;
	for(i = 1; i <= w; i++){
		for(j = 1; j <= h; j++){
			
			f[i][j][1] = i*j;
			
		}
	}
	
	for(i = 1; i <= w; i++){
		for(j = 1; j <= h; j++){
			for(k = 2; k <= min(i*j, m); k++){
				
				f[i][j][k] = INF;
				
				//横着切 
				for(t = 1; t < i; t++){
					for(p = 1; p < k; p++){
						
						f[i][j][k] = min(f[i][j][k], max(f[t][j][p], f[i - t][j][k - p]));
						
					}
				}
				
				//竖着切
				for(t = 1; t < j; t++){
					for(p = 1; p < k; p++){
						
						f[i][j][k] = min(f[i][j][k], max(f[i][t][p], f[i][j - t][k - p]));
						
					}
				} 
			}
		}
	}
}