洛谷日常：P1044 栈(1)

/*洛谷P10044*/
#include <bits/stdc++.h>
#define MAX_N 20
#define ll long long
using namespace std;
int n;
ll f[MAX_N][MAX_N];
ll dfs(int i,int j){
	if(f[i][j]) return f[i][j];
	if(i==0) return 1;//边界
	if(j>0) f[i][j]+=dfs(i,j-1);
	f[i][j]+=dfs(i-1,j+1);
	return f[i][j]; 
}
int main(){
	scanf("%d",&n);
	printf("%lld",dfs(n,0));
	return 0;
}