#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)



typedef long long ll;
ll dp[55];
ll rec(int x) {
	if (0 <= dp[x]) return dp[x];

	if (x == 0) return dp[x] = 1;
	if (x == 1) return dp[x] = rec(0);
	return dp[x] = (rec(x - 1) + rec(x - 2));
}
//-----------------------------------------------------------------
int main() {
	int N; cin >> N;
	rep(i, 0, N + 1) dp[i] = -1;
	cout << rec(N) << endl;
}