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 Rust (1.15.1) (judge verdict: Accepted)

use std::io;
use std::io::{Read, BufReader};
use std::cmp;

macro_rules! read {
    ( $( $t:ty ),* ) => {
        {
            let mut buf = String::new();
            io::stdin().read_line(&mut buf);
            let mut sp = buf.trim().split(" ");
            ($(
                {
                    sp.next().unwrap().parse::<$t>().unwrap()
                },
            )*)
        }
    }
}
macro_rules! read_vec {
    ($t:ty) => {
        {
            let mut buf = String::new();
            io::stdin().read_line(&mut buf);
            let mut sp = buf.trim().split(" ");
            let mut ret = vec![];
            for s in sp {
                ret.push(s.parse::<$t>().unwrap());
            }
            ret
        }
    }
}

fn main() {
    let n = read!(usize);
    let a = read_vec!(i32);
    
    let mut cnt = vec![0; 101010];
    for v in a {
        cnt[v as usize] += 1;
    }

    let mut ret = 0;
    for i in 1..101000 {
        ret = cmp::max(ret, cnt[i - 1] + cnt[i] + cnt[i + 1]);
    }
    println!("{}", ret);
}