#include <bits/stdc++.h>   using namespace std;   bool isprime(long long n) {     if (n < 2) return false;     if (n == 2) return true;     if (n % 2 == 0) return false;     for (int i = 3; i * i <= n; i = i + 2) {       if (n % i == 0) return false;     }     return true;   }   int main() {     int w, h, k;     cin >> w >> h >> k;     int sum = 0;     while (k--) {       sum += (2 * w + (2 * (h - 2)));       w -= 4;       h -= 4;     }     cout << sum;     return 0;   }   