#include <bits/stdc++.h>
using namespace std;

int main(){
  double n,m;
  int d;
  cin >> n >> m >> d;
  double p = (n-(double)d)*2./(n*n);
  if(d == 0) p = 1.0/n;
  cout << fixed << setprecision(9) << p*(m  -1) << endl;
  return 0;
}