#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int K;
main()
{
	cin>>K;
	double ans=0;
	if(K==0)ans=M_PI*M_PI/6;
	else
	{
		for(int N=1;N<=K;N++)ans+=1./N;
		ans/=K;
	}
	cout<<fixed<<setprecision(16)<<ans<<endl;
}