#include<bits/stdc++.h>
#include <atcoder/all>
#ifdef LOCAL
#include <debug_print.hpp>
#define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (static_cast<void>(0))
#endif
using namespace atcoder;
using mint=modint1000000007;
using namespace std;
using ll=long long;
using ul=unsigned long long;
int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1};
int dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};
using Graph=vector<vector<int>>;
ll op(ll a,ll b){return max(a,b);}
ll e(){return 0;}
int main(){
    int k;
    cin>>k;
    double pi=M_PI;
    if(k==0){cout<<fixed<<setprecision(10)<<(pi*pi)/6.0<<endl;return 0;}
    double ans=0.0;
    for(double i=1;i<=k;i++)ans+=1.0/i;
    cout<<fixed<<setprecision(10)<<ans/k<<endl;
}