#coding:utf-8

N=input()
X=map(int,raw_input().split())

X.sort()

s=[X[0]]
for i in range(1,N):
	if X[i]-s[i-1]==2:
		s.append(X[i])
	else:
		s.append(0)

if N%2==0:
	if X==s:
		print N
	else:
		print 0
else:
	print 1