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 <bits/stdc++.h>
#define db double
#define ll long long
#define X first
#define Y second
#define pii pair<int, int>
#define rep(i, x, y) for(int i = x; i <= y; i ++)
#define rrep(i, x, y) for(int i = x; i >= y; i --)
#define REP(i, y) rep(i, 0, y - 1)
#define pb push_back
#define mp make_pair
using namespace std;
inline int read()
{
    int x = 0, f = 1; char ch = getchar();
    while(ch < '0' || ch > '9') {if(ch == '-') f = -1; ch = getchar();}
    while(ch >= '0' && ch <= '9') {x = x * 10 + ch - '0'; ch = getchar();}
    return x * f;
}
int a[100010];
int main()
{
	int n = read();
	rep(i, 1, n)
	{
		int x = read();
		a[x] ++;
	}
	int ans = 0;
	rep(i, 1, 100000)
		ans = max(ans, a[i - 1] + a[i] + a[i + 1]);
    cout << ans;
	return 0;
}