#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    double a = 1,b = 1,c,ans;
    int n;
    cin >> n;
    while(n--)
    {
        c = a + b;
        a = b;
        b = c;
        ans += 1.0 * b / a;
    }
    printf("%.4f",ans);
    return 0;
}