#include<bits/stdc++.h>
using namespace std;
using ll=long long;
int main()
{
    cin.tie(0)->sync_with_stdio(0);
    int k;cin>>k;
    long double ans=0;
    if(k==0)ans=acos(-1)*acos(-1)/6;
    else
    {
        for(long double n=1;n<=k;n++)
        {
            ans+=1/n;
        }
        ans/=k;
    }
    cout<<fixed<<setprecision(15);
    cout<<ans<<endl;
}