C++ :

#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
	int n;
	cin>>n;
	double fz=2,fm=1,sum=0;
	for (int i=1; i<=n; i++)
	{
		sum+=fz/fm;
		double t=fz;
		fz+=fm;
		fm=t;
	}
	printf("%.2lf\n",sum);
	return 0;
}