# include <bits/stdc++.h>
using namespace std;
typedef long long ll; 
// # define int long long
# define lc u << 1
# define rc u << 1 | 1
# define fi first
# define se second

int n;
signed main ()
{
    // freopen ("card.in", "r", stdin); freopen ("card.out", "w", stdout);
    scanf ("%d", &n);
    double ans = 1;
    for (int i = 2; i <= n; i ++ )
    {
        ans += 2.0 / i; // 两边
        if (i > 2)
        {
			double p = ((i - 1) * i / 2) * ((i - 1) * i / 2) - (i - 1) * i * (2 * i - 1) / 6;
			p /= (i - 1) * (i - 2);
			ans += p * (i - 2.0) / i;
		}
	}
    printf ("%.10lf\n", ans);
    return 0;
}