mod = 10**9 + 7
fact = [1] * (10**6 + 1)
inv = [1] * (10**6 + 1)
finv = [1] * (10**6 + 1)
for i in range(2, 10**6 + 1):
    fact[i] = fact[i - 1] * i % mod
    inv[i] = mod - inv[mod % i] * (mod // i) % mod
    finv[i] = finv[i - 1] * inv[i] % mod
def comb(x, y):
    return fact[x] * finv[y] % mod * finv[x - y] % mod

n = int(input())
H = list(map(int, input().split()))

if H[0] == 0:
    print(1)
    exit()
m = len(H)
res = n - sum(H) - (m - 1)
if res < 0:
    print("NA")
    exit()
print(comb(res + m, m))