#include <iostream>
#include <cmath>
using namespace std;

double d,n,m;
int main(){
	cin >> n >> m >> d;
	if(d!=0) printf("%.10f\n",2*(n-d)*(1/n)*(1/n)*(m-1));
	else printf("%.10f\n",n*(1/n)*(1/n)*(m-1));
//	cout <<  << endl;
}