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