mod=1000000007
maxN=1000010
fact=[1]*maxN
for i in range(2,maxN):
    fact[i]=fact[i-1]*i%mod
ifact=[0]*maxN
for i in range(maxN):
    ifact[i]=pow(fact[i],mod-2,mod)
def comb(N,K):
    if K<0 or K>N:
        return 0
    return fact[N]*ifact[K]*ifact[N-K]%mod
N=int(input())
M=list(map(int,input().split()))
if M[0]==0:
    print(1)
    exit()
N-=(len(M)-1)
for i in range(len(M)):
    N-=M[i]
if N<0:
    print('NA')
    exit()
print(comb(N+len(M),len(M)))