#include <bits/stdc++.h>
int main() {
  int N, M, x, ans = 0;
  scanf("%d %d %d", &N, &M, &x);
  for (int i = x; i <= N - x + 1; i++) {
    for (int j = x; j <= M - x + 1; j++) {
      if (((i + j) & 1) == 0 &&
          (i == x || i == N - x + 1 || j == x || j == M - x + 1))
        ans++;
    }
  }
  printf("%d", ans);
  return 0;
}
