#include <stdio.h>
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000
int main(){
	
	double N;
	cin>>N;
	
	cout<<fixed<<setprecision(10)<<riemann_zeta(N)<<endl;
	
	return 0;
}