#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]
w = {e:[] for e in a}

for e in a:
    if e-1 in w:
        w[e-1].append(e)
    w[e].append(e)
print(max(map(len,w.values())))