#include <bits/stdc++.h>
using namespace std;
int n, m, x, g(0);
int main() {
  cin >> n >> m >> x;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
      if (i % 2 == j % 2 && x == min(min(i, n + 1 - i), min(j, m + 1 - j))) g++;
  cout << g;
  return 0;
}
