#include <bits/stdc++.h>
#define MOD 998244353
#define mod 1000000007
#define ll long long
#define ull unsigned long long
#define ui unsigned int
using namespace std;
const int maxn = 1e6+9;
ll a(ll n)
{
    if (n == 1) return 2;
    if (n == 2) return 3;
    return a(n - 1) + a(n - 2);
}
ll b(ll n)
{
    if (n <= 2) return n;
    return b(n - 1) + b(n - 2);
}
int main()
{
	int n;
	cin >> n;
	double ans = 0.0000;
	for (int i = 1; i <= n; i++)
    	ans += (double)(a(i) / b(i));
	printf("%.4lf",ans);
	return 0;
}