Problem:
Score : 300 points

Problem Statement

You are given an integer sequence of length N, a_1,a_2,...,a_N.

For each 1≤i≤N, you have three choices: add 1 to a_i, subtract 1 from a_i or do nothing.

After these operations, you select an integer X and count the number of i such that a_i=X.

Maximize this count by making optimal choices.

Constraints

1≤N≤10^5

0≤a_i<10^5 (1≤i≤N)

a_i is an integer.

Input

The input is given from Standard Input in the following format:

N
a_1 a_2 .. a_N

Output

Print the maximum possible number of i such that a_i=X.

Sample Input 1

7
3 1 4 1 5 9 2

Sample Output 1

4

For example, turn the sequence into 2,2,3,2,6,9,2 and select X=2 to obtain 4, the maximum possible count.

Sample Input 2

10
0 1 2 3 4 5 6 7 8 9

Sample Output 2

3

Sample Input 3

1
99999

Sample Output 3

1

Solution in PyPy3 (2.4.0) (judge verdict: Accepted)

import sys
import math
from fractions import gcd
# import queue
from collections import Counter
# from itertools import accumulate
# from functools import reduce

def lcm(a, b):
    return a * b // gcd(a, b)

def combination_count(n, r):
    return math.factorial(n) // (math.factorial(n - r) * math.factorial(r))

def permutations_count(n, r):
    return math.factorial(n) // math.factorial(n - r)

big_prime = 1000000007

"""
# 標準入力取得
## 文字列
 = sys.stdin.readline().rstrip()
 = list(sys.stdin.readline().rstrip())

## 数値
 = int(sys.stdin.readline())
 = map(int, sys.stdin.readline().split())
 = list(map(int, sys.stdin.readline().split()))
 = [list(map(int,list(sys.stdin.readline().split()))) for i in range(N)]
"""

N = int(sys.stdin.readline())
L = list(map(int, sys.stdin.readline().split()))

LM = list(map(lambda x : x - 1, L))
LP = list(map(lambda x : x + 1, L))

X = LM + L + LP
# print(LM)
# print(L)
# print(LP)
Xc = Counter(X)
# print(Xc.most_common())
print(Xc.most_common()[0][1])