#include <bits/stdc++.h>
using namespace std;
int num(int n){
    int r;
    if(n==1||n==2){
        r=1;
    }
    else{
        r=num(n-1)+num(n-2);
    }
    return r;
}
int main(){
    int v;
    double cnt=0;
    for(int i=1;i<=v;i++){
        cnt+=num(i)*1.0/num(i+1);
    }
    printf("%.3f",cnt);
    return 0;
}
/**************************************************************
	Problem: 1147
	User: luyanchen
	Language: C++
	Result: Wrong Answer
****************************************************************/