import sys

sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


M = I()
H = LI()
K = len(H)
mod = 10**9+7

a = M-sum(H)+1
if a < K:
    print('NA')
    exit()
if H[0] == 0:
    print(1)
    exit()

fac = [1,1]
for i in range(2,a+1):
    fac.append((fac[-1]*i) % mod)

print((fac[a]*pow(fac[K],mod-2,mod)*pow(fac[a-K],mod-2,mod)) % mod)