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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>

int c(const void * d, const void * e)
{
   return ( *(int*)d - *(int*)e );
}
int main()
{
    int i, j, N, max=0, count;
    scanf("%d", &N);
    int a[3*N];
    for(i=0;i<(N*3);i+=3){
        scanf("%d", a+i);
        a[i+1]=a[i]-1;
        a[i+2]=a[i]+1;
    }
    if(N==1)max=1;
    else{

        int current=a[0]+1;
        qsort(a, N*3, sizeof(int), c);
        for(j=0;j<(N*3);j++){
            if(current!=a[j]){
                current=a[j];
                count=1;
            }
            else{
                count+=1;
                if(count>max)max=count;
            }
        }
    }
    printf("%d", max);
    return 0;
}