#include<iostream>
#include<iomanip>
#include<cmath>
#include<cassert>
using namespace std;
const int LIM=(int)1e7+1;
long double H[LIM];
long double calc(long long x)
{
	if(x<LIM)return H[x];
	return log((long double)x)+0.5772156649+0.5/x;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	for(int i=1;i<LIM;i++)H[i]=H[i-1]+(long double)1/i;
	long long N;cin>>N;
	long long l=1;
	long double ans=0;
	while(l<=N)
	{
		long long q=N/l;
		long long r=N/q;
		ans+=(calc(r)-calc(l-1))*calc(q);
		l=r+1;
	}
	cout<<fixed<<setprecision(16)<<ans<<endl;
}