//yukicoder 44
#include <bits/stdc++.h>
#define REP(i,n) for(int (i)=0;(i)<(n);(i)++)
using namespace std;

long long dp[51];

int main() {
	int N;
	cin >> N;
	dp[N] = dp[N - 1] = 1;
	for(int i = N - 2; i >= 0; i--) {
		dp[i] = dp[i + 1] + dp[i + 2];
	}
	cout << dp[0] << endl;
	return 0;
}