#include <iostream>

using namespace std;

int main()
{
  long long n, m, d;
  cin >> n >> m >> d;
  if(d == 0) printf("%.6lf\n", (double)(m - 1) / n);
  else printf("%.6lf\n", (double)(m - 1) * 2 * (n - d) / (n * n));
  
  return 0;
}
