题解

#include <cstdio>

int n, f[30];
int main()
{
scanf("%d", &n);
f[0] = 1, f[1] = 1;
for(int i=2; i<=n; i++)
for(int j=0; j<i; j++)
f[i] += f[j] * f[i-j-1];
printf("%d", f[n]);
return 0;
}