#include<bits/stdc++.h>
using namespace std;
int main(){
    double a=1,b=1,c,s=0;
	int i,n;
	cin>>n;
	for(i=1;i<=n;++i){
		c=a+b;
		a=b;
		b=c;
		s=s+b/a; 
	}
	printf("%0.4lf\n",s);
	return 0;
}