// Update probabilty distribution step by step, taking O(n) per iteration.
// Timed to stop after ~0.9 seconds, then uses the current distribution as an estimate.
#include <bits/stdc++.h>
using namespace std;

int main() {
	clock_t start = clock();

	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;
	}
	
	vector<double> prob(n+1);
	prob[i] = 1;
	
	while (k--) {
		vector<double> nprob(n+1);
		double s = 0;
		for (int b = 1; b <= n; b++) {
			s += prob[b];
			nprob[b] = (b-1)*prob[b] + s*(h[n]-h[b-1]);
		}
		double t = 0;
		for (int b = n; b >= 1; b--) {
			nprob[b] = (nprob[b] + t)/n;
			t += prob[b]*(h[n]-h[b-1]);
		}
		swap(prob,nprob);

		if (double(clock()-start)/CLOCKS_PER_SEC > 0.9) break;
	}

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