栈

#include<cstdio>
using namespace std;
int n,f[18][18];
int main()
{
	scanf("%d",&n);
	for(int i=0;i<=n;i++){
		for(int j=0;j<=n-i;j++){
			if(!i)f[i][j]=1;
			else if(!j)f[i][j]=f[i-1][1];
			else f[i][j]=f[i-1][j+1]+f[i][j-1];
		}
	}printf("%d\n",f[n][0]);
	return 0;
}
/*
Sample input:
3
Sample output:
5

in1:
1
out1:
1

in2:
3
out2:
5

in3:
9
out3:
4892

in4:
15
out4:
9694845

in5:
18
out5:
477638700
*/