#include<bits/stdc++.h>
using namespace std;
int main()
{
	int N;
	double t,n,ans;
	double f[70];
	f[0] = 0;
	f[1] = 1;
	cin>>N;
	for(int i = 2;i <= 50;i++)
	{
		f[i] = f[i - 1] + f[i - 2];
	}
	ans = f[N];
	printf("%.2llf",ans);
	return 0;
}