#include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007

int main() {

  double m,n,d;
  cin >> n >> m >> d;

  cout << fixed << setprecision(10);
  if(d == 0) cout << (m-1) / n << endl;
  else cout << 2*(n-d)*(m-1) / (n*n) << endl;
  
}
