#!/bin/python3

import sys


n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]

a.sort()
b = []
i = 0
while i < len(a):
    j = i+1
    x = 1
    while j < len(a) and a[j] == a[i]:
        x += 1
        j += 1
    b.append((x, a[i]))
    i = j

sol = 0
for i in range(0, len(b) - 1):
    if b[i+1][1] - b[i][1] == 1:
        sol = max(sol, b[i][0] + b[i+1][0])
    else:
        sol = max(sol, b[i][0])
sol = max(sol, b[-1][0])
    
print(sol)