#include<bits/stdc++.h>
using namespace std;
#define ll long long 

ll dfs(ll n)
{
	if(n == 1)
	{
		return 1;
	}
	else if(n == 2)
	{
		return 2;
	}
	else
	{
		return dfs(n-1) + dfs(n-2) ;
	}
 } 

int main()
{
	int n;
	cin>>n;
	cout<<dfs(n);
}