import sys
Mod = 10 ** 9 + 7
Len = int(input())
A = list(map(int, input().split()))
R = Len - sum(A)

if A[0] == 0:
    print(1)
    sys.exit()
if len(A) - 1 > R:
    print("NA")
    sys.exit()

N = R + 1
K = min(len(A), N - len(A))
ans = 1

for i in range(K):
    ans = ans * (N - i) % Mod
    ans = ans * pow(i + 1, Mod - 2, Mod) % Mod

print(ans)