#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main(){
    int n;cin>>n;
    if(n==0){
        cout << fixed << setprecision(10) << ((double)acos(-1)*acos(-1))/(double)6 << endl;
        return 0;
    }
    double ans = 0;
    for(int i = 1; n >= i; i++){
        ans += (double)1/(double)i;
    }
    cout << fixed << setprecision(10) << (double)ans/(double)n << endl;
}