#include<stdio.h>
int f(int n){
	if(n==1||n==2){
		return 1;
	}else{
		return f(n-1) + f(n-2);
	}
}
void main(){
	int n,i;
	scanf("%d",&n);
	double s = 0;
	for(i=1;i<=n;i++){
		s = s + f(i)*1.0/f(i+1);
	}
	printf("%.3lf",s);
}

/**************************************************************
	Problem: 1147
	User: admin
	Language: C
	Result: Accepted
	Time:10 ms
	Memory:1144 kb
****************************************************************/