#!/bin/python

import sys


n = int(raw_input().strip())
a = map(int,raw_input().strip().split(' '))

a = sorted(a)

last = 0
curr = 1
best = 0

for i in xrange(1, len(a)):
    if a[i] == a[i-1]: curr += 1
    elif a[i] == a[i-1] + 1:
        best = max(best, last + curr)
        last = curr
        curr = 1
        i = i + 1
    else:
        best = max(best, last + curr)
        last = 0
        curr = 1
best = max(best, last + curr)
        
print best