#include<bits/stdc++.h>
using namespace std;
int aws[1000]={0};
double ans[1000]={0};
int main(){
	int n,i;
	aws[0]=1;
	aws[1]=2;
	ans[0]=0;
	ans[1]=2;
	for(i=2;i<1000;i++){
		aws[i] = aws[i-1] + aws[i-2];
		ans[i] = ans[i-1] + (double)aws[i]/(double)aws[i-1];
	}
	cin>>n;
	printf("%.2f",ans[n]);
	return 0;
	
}