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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include<map>
#include<cmath>
#include<stdlib.h>
#include<algorithm>
#include<set>
#include<vector>
#include<queue>

using namespace std;

typedef pair<int,int> pii;
typedef long long ll;

const int MX = 100005;

int N;
int D[MX];

int main()
{
	scanf("%d", &N);
	for(int i = 1; i <= N; i++){
		int a;
		scanf("%d", &a);
		D[a] ++;
	}
	int ans = 0;
	for(int i = 1; i+1 < MX; i++){
		ans = max(ans, D[i-1] + D[i] + D[i+1]);
	}
	printf("%d\n", ans);
}