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 cmp(const void *a,const void *b){
  return *(int*)a - *(int*)b;
}

int main(){
  int n = 0;
  int a[100000] = {};
  int b[100000] = {};
  int i = 0;
  long max = 0;
  scanf("%d",&n);
  for(i=0;i<n;i++){
    scanf("%d",&a[i]);
    b[a[i]-1]++;
  }
  for(i=0;i<100000;i++){
    if(i != 0 && i != 99999){
      if(b[i-1]+b[i]+b[i+1] > max){
        max = b[i-1]+b[i]+b[i+1];
        //printf("%d/",b[i-1]+b[i]+b[i+1]);
      }
      
    }else if(i == 0){
      if(b[0] + b[1] > max){
        max = b[0] + b[1];
      }
    }else if(i == 99999){
      if(b[99998]+b[99999] > max){
        max = b[99999]+b[99998] ;
      }
    }
  }
  printf("%ld",max);
    
  /*for(i=0;i<n-1;i++){
    printf("%d ",b[i]);
  }*/
  return 0;
}