MOD = 10 ** 9 + 7

m = int(input())
H = list(map(int, input().split()))
if H == [0]:
    print(1)
    exit()
n = len(H)
m -= sum(H) + len(H) - 1
if m < 0:
    print("NA")
    exit()
def nCk(n, k):
    if k > n or k < 0:
        return 0
    ret = 1
    for i in range(n, n - k, -1):
        ret *= i
        ret %= MOD
    inv = 1
    for i in range(1, k + 1):
        inv *= i
        inv %= MOD
    return ret * pow(inv, MOD - 2, MOD) % MOD

def nHk(n, k):
    if n == k == 0:
        return 1
    return nCk(n + k - 1, k)

print(nHk(1 + len(H), m))