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

int main()
{
	int n;
	cin >> n;
	vector<int64_t> dp(n + 1);
	dp[0] = 1;
	for(int i = 0; i < n; i++)
	{
		if(i + 1 <= n) dp[i + 1] += dp[i];
		if(i + 2 <= n) dp[i + 2] += dp[i];
	}
	cout << dp[n] << endl;
	return 0;
}