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


int main()
{
    int n,m,c,row,col,x,ans;
    while(cin>>n>>m>>c && n)
    {
         row=n-7;
         col=m-7;
         x=row*col;
        if(c==1 && x%2)
              ans=(x+1)/2;
        else
            ans=x/2;
        cout<<ans<<endl;
    }
    return 0;
}