N = int(input())
A = list(map(int, input().split()))
ans = 1

for i in range(1, N + 1):
    ans = ans * i

for i in range(1, 21):
    cnt = 0
    for a in A:
        if a == i:
            cnt = cnt + 1
    for j in range(1, cnt + 1):
        ans = ans // j
print(ans)