#include <bits/stdc++.h>

using namespace std;

#define INF 2000000000
#define MOD 1000000007
typedef long long ll;
typedef pair<int, int> P;


int ret = 0;
int N;

int main()
{
	cin >> N;
	ll dp[N+1];
	dp[0] = 1;
	dp[1] = 1;
	dp[2] = 2;
	for (int i = 3; i <= N; i++) {
		dp[i] = dp[i-1] + dp[i-2];
	}
	cout << dp[N] << "\n";
}