#include <stdio.h>
#define _USE_MATH_DEFINES
#include <math.h>
#include <vector>
#include <algorithm>

using namespace std;

int main(){
    long n,m,d;
    scanf("%ld %ld %ld", &n, &m, &d);
    long k;
    if(d == 0){
        k = n;
    }
    else{
        k = 2 * (n - d);
    }
    k = k * (m - 1);
    double dAns = double(k)/double(n * n);
    printf("%.10lf", dAns);
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
	ll n, m, d;
	cin >> n >> m >> d;
	cout << fixed << setprecision(20);
	double ans = 0;
	for (int i = 0; i < m - 1; i++) {
		ans += (double)((double)(2 * n - 2 * d) / n) / n;
	}
	if (d == 0)ans *= 0.5;
	cout << ans << endl;
}