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

int main() {
    double N, M, D;
    cin >> N >> M >> D;
    double A = 2 * (N - D);
    if(D == 0) A = N;
    double B = A / (N * N);
    double C = B * (M - 1);
    printf("%.10lf\n", C);
    return 0;
}
