#include<cstdio> #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; }