#include <bits/stdc++.h>
typedef long long ll;
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,a) FOR(i,0,a)
	
using namespace std;
const int MAX_N=50;
int N;
ll dp[MAX_N+1];
int main(){
	cin>>N;
	dp[N]=1;
	for(int i=N-1;i>=0;i--){
		dp[i]=dp[i+1];
		if(i+2<=N){
			dp[i]+=dp[i+2];
		}
	}
	cout<<dp[0]<<endl;
}