// Update probability distribution step by step, total runtime O(k*n*n).
#include <bits/stdc++.h>
using namespace std;

int main() {
	int n, i, k;
	cin >> n >> i >> k;

	vector<double> h(n+1);
	for (int a = 1; a <= n; a++) {
		h[a] = h[a-1] + 1.0/a;
	}

	auto trans = [&](int a, int b) {
		double sum = a == b ? a-1 : 0;
		sum += h[n] - h[max(a,b)-1];
		return sum/n;
	};
	
	vector<double> prob(n+1);
	prob[i] = 1;
	
	while (k--) {
		vector<double> nprob(n+1);
		for (int a = 1; a <= n; a++) {
			for (int b = 1; b <= n; b++) {
				nprob[b] += trans(a,b) * prob[a];
			}
		}
		swap(prob,nprob);
	}

	double E = 0;
	for (int a = 1; a <= n; a++) E += a*prob[a];
	cout << fixed << setprecision(20) << E << endl;
}