#include<cstdio>
#include<stdlib.h>
int main()
{
int n,m,c;
while(scanf("%d%d%d",&n,&m,&c),(m+n+c))
int p,q;
p=n-7;
q=m-7;
if((p*q)&1)
printf("%d\n",(p*q)/2+c);
else
printf("%d\n",(p*q)/2);
}
return 0;