#!/bin/env python


def get_input():
    size = raw_input().strip()
    data = [int(x) for x in raw_input().strip().split()]
    return size, data


def do_the_thing(data):
    i = int()
    answer = int()
    for n in set(data):
        i = 0
        i += data.count(n)
        i += data.count(n-1)
        if i > answer:
            answer = i
    return answer


def main():
    size, data = get_input()
    print do_the_thing(data)


if __name__ == '__main__':
    main()