#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, x, pat, res[10000], ind = 0, t;
  cin >> n >> m >> x;
  x--;
  if (n < m) {
    t = n;
    n = m;
    m = t;
  }
  while (n > 2 && m > 2) {
    res[ind] = n + m - 2;
    ind++;
    n -= 2;
    m -= 2;
  }
  if (n > m) {
    if (n > 2) {
      pat = n + m - 2;
      res[ind] = pat;
    } else {
      res[ind] = 1;
    }
  } else {
    if (n == 2) {
      res[ind] = 2;
    } else {
      res[ind] = 1;
    }
  }
  if (ind < x)
    cout << "0";
  else
    cout << res[x];
  return 0;
}
