#include <bits/stdc++.h>

using namespace std;

int main() {
    long double n, m, d;
    cin >> n >> m >> d;

    cout.setf(ios::fixed);
    cout.precision(10);
    cout << (m - 1) * (1 + (d != 0)) * (n-d) / pow(n, 2) << endl;

    return 0;
}