#include<bits/stdc++.h>
using namespace std;
long long ans;
int main(){
	int n,m,d;
	scanf("%d%d%d",&n,&m,&d);
	ans=(n-d)*2*(long long)(m-1);
	if(d==0) ans/=2;
	double sum=ans/(double)(n*(long long)n);
	printf("%.10f\n",sum);
	return 0;
}
