#include<iostream>
#include<cmath>
#include<algorithm>
#include<string>
#include<map>
using namespace std;
int main() {
    double a = 2, b = 1, sum = 0, c;
    int n;
    cin >> n;
    for (int i = 0; i < n;i++) {
        sum += a / b;
        c = a;
        a = a + b, b = c;
    }
    printf("%.2lf", sum);
    return 0;
}