我竟然是首A，来发个题解吧，这题一定要开long long(可把我坑惨了...

#include <iostream>
#define int long long
using namespace std;
int a[10005];
long long func(int x){
	long long sum=0;
	if(a[x]!=0) return a[x];
	else for(int i=2;i<=x-1;i++) sum=sum+func(i)*func(x-i+1);
	return a[x]=sum;
} 
signed main(){
        int n;
	a[2]=1,a[3]=1;
	cin>>n;
	cout<<func(n)<<endl;
	return 0;
}