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;

fn main() {
    let mut buffer = String::new();
    io::stdin().read_line(&mut buffer).unwrap();
    buffer.clear();
    io::stdin().read_line(&mut buffer).unwrap();
    let xs: Vec<i32> = buffer
        .split_whitespace()
        .map(|x| x.parse().unwrap())
        .collect();
    let mut ys = Vec::with_capacity(3 * xs.len());
    for x in xs.into_iter() {
        ys.push(x);
        ys.push(x+1);
        ys.push(x-1);
    }
    ys.sort();
    let mut m = 0;
    let mut prev = &ys[0];
    let mut cnt = 0;
    for i in 0..ys.len() {
        if &ys[i] == prev {
            cnt += 1;
        } else {
            if m < cnt {
                m = cnt
            }
            prev = &ys[i];
            cnt = 1;
        }
    }    
    println!("{}", m);
}