#include <bits/stdc++.h>
using namespace std;
vector<int> v1, v2;
int a[1000000];
int main() {
  int n, m, t;
  cin >> n >> m >> t;
  if (m < n) swap(m, n);
  while ((n > 0) && (m > 0)) {
    if (m == 1 && n == 1)
      v1.push_back(1);
    else if (n == 1)
      v1.push_back((m + 1) / 2);
    else
      v1.push_back(((n % 2) ? ((m + 1) / 2) * 2 : m) +
                   ((m % 2) ? ((n - 2) / 2) * 2 : max(n - 2, 0)));
    n -= 2;
    m -= 2;
  }
  if (t > (int)v1.size())
    cout << 0 << endl;
  else
    cout << v1[t - 1] << endl;
  return 0;
}
