#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;


int main(){
    int k;
    cin >> k;
    if(k==0){
        cout << setprecision(20) << PI*PI/6 << endl;
        return 0;
    }
    double ans = 0;
    for(int i=1;i<=k;i++){
        ans += 1 /(double)i;
    }
    ans /= k;
    cout << setprecision(20) << ans << endl;
    return 0;
}