mod = 1000000007

x = input()
a = map(int,raw_input().split())
l = len(a)

x += sum([1-a[i] for i in xrange(l)])

if a[0] == 0:
	print 1
elif x < l*2-1:
	print "NA"
else:
	d = 1
	for i in xrange(l+1,x-l+2):
		d *= i*pow(i-l,mod-2,mod)
		d %= mod
	print d