#include<iostream>
#include<vector>
#include<map>
#include<cassert>
#include<iomanip>
using namespace std;
int gcd(int a,int b)
{
	while(b)
	{
		int t=a%b;
		a=b;
		b=t;
	}
	return a;
}
map<int,long double>memo;
long double solve(int N)
{
	if(N==1)return 0;
	if(memo.find(N)!=memo.end())return memo[N];
	vector<int>to(N,1);
	for(int g=2;g<N;g++)if(N%g==0)for(int i=g;i<N;i+=g)to[i]=g;
	long double ans=0;
	for(int i=1;i<N;i++)ans+=solve(to[i]);
	ans+=N;
	ans/=N-1;
	return memo[N]=ans;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int N;cin>>N;
	cout<<fixed<<setprecision(16)<<solve(N)<<endl;
}