uva 10790 How Many Points of Intersection?

#include <stdio.h>

int case_count;

long long func(int m, int n)
{
return (long long)(m)*(long long)(n)*(long long)(m-1)*(long long)(n-1) / 4;
}

int main(void)
{
int m, n;

case_count = 0;
while(1)
{
scanf("%d %d", &m, &n);
if(!m && !n)
break;
case_count ++;
printf("Case %d: %lld\n", case_count, func(m,n));
}

return 0;
}