import sys
def solve():
    data = sys.stdin.read().split()
    n = int(data[0])
    a = [0] * (n + 1)
    for i in range(1, n + 1):
        v = int(data[i])
        a[v] += 1
    ans = 1
    for i in range(1, n + 1):
        ans *= i
    for i in range(1, n + 1):
        if a[i] > 1:
            for j in range(2, a[i] + 1):
                ans //= j
    print(ans)

if __name__ == '__main__':
    solve()