#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <cmath>
using namespace std;

int main()
{
	long long n, m, d;
	double ans;
	cin >> n >> m >> d;
	if (d != 0)
		ans = 1.0 * 2 * (n - d) / n*(m - 1) / n;
	else
		ans = 1.0*(n - d)/n*(m - 1) / n;
	printf("%.7lf\n", ans);
	return 0;
}