N = int(input())
A = [int(input()) for _ in range(N)]
A.sort()
flag = False
for i in range(N - 1):
    now, nex = A[i], A[i + 1]
    if nex - now == 1:
        flag = True
        break

if flag:
    ans = 2
else:
    ans = 1
print(ans)