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)

//! https://github.com/hatoo/competitive-rust-snippets
//!
//! MIT License
//!
//! Copyright (c) 2018 hatoo
//!
//! Permission is hereby granted, free of charge, to any person obtaining a copy
//! of this software and associated documentation files (the "Software"), to deal
//! in the Software without restriction, including without limitation the rights
//! to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//! copies of the Software, and to permit persons to whom the Software is
//! furnished to do so, subject to the following conditions:
//!
//! The above copyright notice and this permission notice shall be included in all
//! copies or substantial portions of the Software.
//!
//! THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//! IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//! FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//! AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//! LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//! SOFTWARE.
#![allow(unused_imports, unused_macros, dead_code)]
use std::cmp::{max, min, Ordering};
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
use std::io::{stdin, stdout, BufWriter, Write};
use std::iter::FromIterator;
mod util {
    use std::fmt::Debug;
    use std::io::{stdin, stdout, BufWriter, StdoutLock};
    use std::str::FromStr;
    pub fn line() -> String {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.trim().to_string()
    }
    pub fn chars() -> Vec<char> {
        line().chars().collect()
    }
    pub fn gets<T: FromStr>() -> Vec<T>
    where
        <T as FromStr>::Err: Debug,
    {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.split_whitespace()
            .map(|t| t.parse().unwrap())
            .collect()
    }
    pub fn with_bufwriter<F: FnOnce(BufWriter<StdoutLock>) -> ()>(f: F) {
        let out = stdout();
        let writer = BufWriter::new(out.lock());
        f(writer)
    }
}
macro_rules !get {([$t :ty ] ) =>{{let mut line :String =String ::new () ;stdin () .read_line (&mut line ) .unwrap () ;line .split_whitespace () .map (|t |t .parse ::<$t >() .unwrap () ) .collect ::<Vec <_ >>() } } ;([$t :ty ] ;$n :expr ) =>{(0 ..$n ) .map (|_ |get !([$t ] ) ) .collect ::<Vec <_ >>() } ;($t :ty ) =>{{let mut line :String =String ::new () ;stdin () .read_line (&mut line ) .unwrap () ;line .trim () .parse ::<$t >() .unwrap () } } ;($($t :ty ) ,*) =>{{let mut line :String =String ::new () ;stdin () .read_line (&mut line ) .unwrap () ;let mut iter =line .split_whitespace () ;($(iter .next () .unwrap () .parse ::<$t >() .unwrap () ,) *) } } ;($t :ty ;$n :expr ) =>{(0 ..$n ) .map (|_ |get !($t ) ) .collect ::<Vec <_ >>() } ;($($t :ty ) ,*;$n :expr ) =>{(0 ..$n ) .map (|_ |get !($($t ) ,*) ) .collect ::<Vec <_ >>() } ;}
macro_rules !debug {($($a :expr ) ,*) =>{eprintln !(concat !($(stringify !($a ) ," = {:?}, " ) ,*) ,$($a ) ,*) ;} }
const BIG_STACK_SIZE: bool = true;
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}
fn solve() {
    let n = get!(usize);
    let a = get!([i64]);
    let mut cnt = vec![0; 100000 + 100];
    for i in 0..n {
        let t = a[i] as usize + 1;
        cnt[t - 1] += 1;
        cnt[t] += 1;
        cnt[t + 1] += 1;
    }
    cnt.sort();
    cnt.reverse();
    println!("{}", cnt[0]);
}