#include <iostream>
#include <cmath>
using namespace std;
int f,n,k;
double solve(int a,int b){
	double F = f,I = a,N = n,ret;
	ret = pow((F - I)/F,b)*pow(I/F,n - b);
	for(int j=0;j<b;j++){
		double J = j;
		ret *= (N - J)/(J + 1);
	}
	return ret;
}

int main(){
	cout.precision(20);
	int i,j;
	cin >> f >> n >> k;
	double ans = 0;
	for(i=0;i<f;i++){
		for(j=k;j<=n;j++){
			ans += solve(i,j);
		}
	}
	cout << ans << endl;
}