#include<bits/stdc++.h>
using namespace std;
int n;
float s=0;
int f(int n){
    int r;
    if(n==1||n==2) r=1;
    else r=f(n-1)+f(n-2);
     
    return r;
     
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        s=s+f(i)*1.0/f(i+1); 
    }
    printf("%.3f",s);
 
    return 0;
}
 
 
 

/**************************************************************
	Problem: 1147
	User: fuyijun
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2076 kb
****************************************************************/