#include<bits/stdc++.h>

using namespace std;

int main()
{
	double ans = 0;
	int n, m, d;
	cin >> n >> m >> d;
	printf("%.8f", 1.0 * (2 * n - 2 * d) / (1ll * n * n) * (m - 1) * (0.5 * (d == 0 ? 1 : 2)));
	return 0;
}
