60pts救

#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll n,ans;
ll a[5005];
ll solve(ll n){
	if(n==0){
		return 1;
	}else if(n<0)return 0;
	ll ans=0;
	if(a[n-1]!=0)ans+=a[n-1];
	else{
		a[n-1]=solve(n-1);
		ans+=a[n-1];
	}
	if(a[n-2]!=0)ans+=a[n-2];
	else{
		a[n-2]=solve(n-2);
		ans+=a[n-2];
	}
	return ans;
}
int main(){
	cin>>n;
	ans=solve(n);
	cout<<ans;
	return 0;
}