#include <iostream>
using namespace std;

int best[21][21][21]; 

int getBest(int w, int h, int m) {
  if (best[w][h][m] > 0)
    return best[w][h][m];
  if (m == 1)
    return w*h;

  int x = 20*20;
  for (int t = 0; t < 2; t++) {
    for (int i = 1; i <= w-1; i++)
      for (int j = 1; j <= m-1; j++) {
	int y1 = getBest(i, h, j);
	int y2 = getBest(w-i, h, m-j);
	y1 >?= y2;
	x <?= y1;
      }
      
    int temp = w;
    w = h;
    h = temp;
  }

  best[w][h][m] = x;
  return x;
}

int main() {
  int w, h, m;
  while (1) {
    cin >> w >> h >> m;
    if (w*h*m == 0)
      return 0;
    cout << getBest(w,h,m) << endl;
  }
}