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<string.h>
#include<stdlib.h>
#include<math.h>

#define mod 1000000007
#define limit 200001
typedef long long ll;
typedef long double ld;
#define rep(i,n) for(i = 0; i < n; i++)
#define max(a,b) {if(a>b){return a;}return b;}
#define min(a,b) {if(a<b){return a;}return b;}
int up_int(const void *a, const void *b){return *(int*)a - *(int*)b;}
int down_int(const void *a, const void *b){return *(int*)b - *(int*)a;}
int up_char(const void *left, const void *right) {return strcmp((char *)left,(char *)right);}

int main(){
    int n,i;
    int a[100001];
    int count[100001];
    int tmp = 0;
    int max = 0;
    int ans;
    
    scanf("%d",&n);
    rep(i,n) scanf("%d",&a[i]);
    rep(i,n) count[a[i]]++;
//    rep(i,n) printf("%d ",a[i]);
//    printf("\n");
//    rep(i,n) printf("%d ... %d\n",i,count[i]);
    
    for(i = 0; i < 99999; i++){
        tmp = count[i] + count[i+1] + count[i+2];
        if(tmp > max){
            max = tmp;
//            printf("%d is good ... %d\n",i,max);
        }
    }
    printf("%d\n",max);
    return 0;
}