#include<bits/stdc++.h>
using namespace std;
int main(){
  double n,m,d;
  cin>>n>>m>>d;
  if(d == 0){
    cout << (1/n)*(m-1) << endl;
  }
  else{
    cout << setprecision(10) << (2*(n-d))*(m-1)/(n*n)<< endl;
  }
  return 0;
}
