a=int(input())
f=[0 for i in range(a+5)]
f[0]=1
for i in range(1,a+1,1):
    f[i]=f[i-1]*i
ans=f[a-2]
d=input().split
for i in range(0,a,1):
    ans=ans//f[int(d[i])-1]
print(ans)

为什么RE