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

int main()
{
	int n;
	cin>>n;
	ll arr[2];
	arr[0] = 1;
	arr[1] = 2;
	for(int i = 0;i<n-2;i++)
	{
		if(i % 2 == 0)
		{
			arr[0] += arr[1];
		}
		else
		{
			arr[1] += arr[0];
		}
	 }
	if(n == 1)
	 	cout<<1;
	else
		cout<<max(arr[0],arr[1]);
}