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

#define pb         push_back

typedef long long ll;
const ll INF = 1000000000000000000ll;
const ll MOD = 1000000007ll;
const double EPS = 1e-8;

ll dp[100][100];

int main(void) {
	//ios_base::sync_with_stdio(false);
	//cin.tie(0);
	
	int n;
	cin >> n;

	dp[0][0] = 1;
	for(int i=1; i<=n; i++){
		for(int j=n; j>=0; j--){
			dp[i][j] = 0;
			if(j-1 >= 0){
				dp[i][j] += dp[i-1][j-1];
			}
			if(j-2 >= 0){
				dp[i][j] += dp[i-1][j-2];
			}
		}
	}

	/*
	for(int j=0; j<=n; j++){
		for(int i=0; i<=n; i++){
			printf("%d ", dp[j][i]);
		}
		puts("");
	}
	*/

	ll ans = 0;
	for(int i=0; i<=n; i++){
		ans += dp[i][n];
	}

	cout << ans << endl;
	
	return 0;
}