#include <iostream>
#include <cstdio> 
#define sc scanf
#define pr printf
using namespace std;

int n;
int f[1005];

int main()
{
	sc ("%d",&n);
	f[1]=1;
	f[2]=2;
	
	for (int i=3; i<=n; i++)
	{
		f[i]=f[i-1]+f[i-2];
	}
	
	if (n!=0)
	{
		pr ("%d",f[n]);
	}	
	else if (n==0)
	{
		pr ("0");	
	}	
	return 0;
}