#include <map>
#include <cmath>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define F(i,j,k) for (int i=j;i<=k;++i)
#define D(i,j,k) for (int i=j;i>=k;--i)
#define ll long long
#define mp make_pair
 
int n; ll ans; 
 
int main()
{
    scanf("%d",&n);
    printf("%.9lf\n",(double)(n/2.0/(2*n-1)*(n+1)));
}