#include <bits/stdc++.h>
using namespace std;
float ss(int n){
    float r;
    if(n==1||n==2){
        r=1.0;
    }
    else{
        r=ss(n-1)+ss(n-2);
    }
    return r;
}
int main(){
    int n,i;
    float s=0.0,k=1.0;
    cin>>n;
    for(i=2;i<=n+1;i++){
        s+=k/ss(i);
        k=ss(i);
    }
    printf("%.3f",s);
    return 0;
}
/**************************************************************
	Problem: 1147
	User: lijinkai
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/