Orz Freopen大佬
fac = [0]*1005 def C(n, m): return fac[n] // fac[m] // fac[n-m] n = int(input()) fac[0] = 1 for i in range(1, n+1): fac[i] = fac[i-1] * i ans = 0 for i in range(2, n//2+1): ans += C(n, 2*i) * C(2*i-1, i+1) print(ans)