#include<cstdio>

int n,m,d;

int main(){
	scanf("%d%d%d",&n,&m,&d);
	double x=2.0*(n-d)/((long long)n*n)*(m-1);
	if(d==0){
		printf("%.10lf",(double)(m-1)/n);
	}
	else printf("%.10lf",x);
	return 0;
}