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)

#define _USE_MATH_DEFINES
#include<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3f
#define MOD 1000000007
#define EPS (1e-10)
typedef long long ll;
typedef pair<int, int>P;
#define int long long

int a[100000];
int sum[500000];
signed main() {
	int n; scanf("%lld", &n);
	rep(i, n) {
		scanf("%lld", &a[i]);
		sum[a[i]]++;
	}
	int Max = 0;
	for (int i = -1; i <= 200000; i++) {
		int cnt = 0;
		if (i - 1 >= 0)cnt += sum[i - 1];
		if (i >= 0)cnt += sum[i];
		cnt += sum[i + 1];

		Max = max(Max, cnt);
	}
	cout << Max << endl;
}