#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5005;
int n, m, k, ans;
int main() {
  scanf("%d %d %d", &n, &m, &k);
  ans = 0;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++) {
      if ((i + j) & 1) continue;
      int x = min(min(i, n - i - 1), min(j, m - j - 1)) + 1;
      ans += x == k;
    }
  printf("%d\n", ans);
  return 0;
}
