#include <iostream>
using namespace std;
#define FOR(i,s,e) for(int i = (s);i <= (e);i++)
int N;

typedef long long ll;

ll dp[60];
int main()
{
	cin >> N;
	dp[0] = 1;
	FOR(i,0,N)
	{
		dp[i + 1] += dp[i];
		dp[i + 2] += dp[i];
	}

	cout << dp[N] << endl;
	return 0;
}