#include <iostream>
using namespace std;

const int MAXM = 400;
int largest[21][21][MAXM + 1];

int get_largest(int w, int h, int m)
{
  if (w > h)
    return largest[h][w][m];
  else
    return largest[w][h][m];
}

int set_largest(int w, int h, int m, int value)
{
  if (w > h)
    largest[h][w][m] = value;
  else
    largest[w][h][m] = value;
}

void fill_largest()
{
  for (int m = 1; m <= MAXM; ++m)
    for (int w = 1; w <= 20; ++w)
      for (int h = 1; h <= w; ++h)
      {
        if (m == 1)
        {
          set_largest(w, h, m, w * h);
          continue;
        }
        
        int smallest = INT_MAX;
        for (int x = 1; x <= ((w + 1) / 2); ++x)
          if ((w - x) >= 1)
          {
            for (int mm = 1; mm < m; ++mm)
              if (get_largest(x, h, mm) &&
                  get_largest(w - x, h, m - mm))
                smallest = min(smallest, max(get_largest(x, h, mm),
                                             get_largest(w - x, h, m - mm)));
            
          }
        for (int y = 1; y <= ((h + 1) / 2); ++y)
          if ((h - y) >= 1)
          {
            for (int mm = 1; mm < m; ++mm)
              if (get_largest(w, y, mm) &&
                  get_largest(w, h - y, m - mm))
                smallest = min(smallest, max(get_largest(w, y, mm),
                                             get_largest(w, h - y, m - mm)));
            
          }
        
        if ((smallest == INT_MIN) || (smallest == INT_MAX))
          set_largest(w, h, m, 0);
        else
          set_largest(w, h, m, smallest);
      }
}

int main()
{
  fill_largest();
#if 0
  for (int m = 1; m <= 4; ++m)
  {

  for (int h = 1; h <= 4; ++h)
  {
    for (int w = 1; w <= 4; ++w)
      cout << get_largest(w, h, m) << " ";
    cout << endl;
  }
  cout << endl;
  }
#endif
  while (true)
  {
    int w, h, m;
    cin >> w;
    cin >> h;
    cin >> m;
    if ((w == 0) && (h == 0) && (m == 0))
      break;

    cout << get_largest(w, h, m) << endl;
  }
  return 0;
}