#include <cstdio>

int main(){
	int n, m;
	int x = 0, y = 0, d;
	
	scanf("%d%d%d", &n, &m, &d);
	
	for (int i=1; i<=n; i++) x += d;
	for (int i=1; i<=m; i++) y += d;
	
	printf("%d\n", x - y);
	return 0;
}