#include <bits/stdc++.h>
using namespace std;
int main()
{
	int n,n1=1,n2=1,n3;
    double f;
	scanf("%d",&n);
	
	for(int i=3;i<=n;i++)
{
		n3=n1+n2;
		n1=n2;
		n2=n3;
		f=n3;
}
		printf("%.2f\n",f);

	return 0;
}