#include <bits/stdc++.h>   using namespace std;   int main() {     int w, h, k;     cin >> w >> h >> k;     int s = 0;     w -= 2;     for (int i = 0; i < k; i++) {       s += (w + h) * 2;       w -= 4;       h -= 4;     }     cout << s;   }   