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

typedef long long Int;
#define REP(i,n) for(int (i)=0;(i)<(int)(n);++(i))

int main() {
	Int dp[55] = {};
	dp[0] = 1;
	for (int i = 0; i < 50; i++) {
		for (int j = 1; j <= 2; j++) {
			dp[i + j] += dp[i];
		}
	}
	int N; cin >> N;
	cout << dp[N] << endl;

}