N = int(input())
Alist = []
for _ in range(N):
    a = int(input())
    Alist.append(a)

Alist.sort()

a = Alist[0]
cnt = 1
for i in range(1, N):
    if Alist[i] == a+1:
        cnt += 1
        break
    a = Alist[i]
print(cnt)