from collections import Counter
input()
N = Counter(map(int, raw_input().split()))
ans = 0
for num in N:
    # print num    
    big = N.get(num + 1, 0)
    small = N.get(num - 1, 0)
    cnt = big if big > small else small
    total = cnt + N[num]
    # print total, cnt
    ans = total if total > ans else ans
print ans