#include<iostream>
#include<cstring>
using namespace std;
int main()
{
	int n;
	cin >> n;
	int* a = new int[n];
	int* b = new int[n];
	a[0] = 1, b[0] = 2;
	double ans = 2.0;
	for (int i = 1; i < n; i++) {
		a[i] = b[i-1];
		b[i] = a[i-1] + b[i-1];
		ans += 1.0*b[i]/a[i];
	}
	printf("%.2f\n", ans);
	return 0;
}