Problem:
Score : 200 points

Problem Statement

We have a sequence p = {p_1,\ p_2,\ ...,\ p_N} which is a permutation of {1,\ 2,\ ...,\ N}.

You can perform the following operation at most once: choose integers i and j (1 \leq i < j \leq N), and swap p_i and p_j. Note that you can also choose not to perform it.

Print YES if you can sort p in ascending order in this way, and NO otherwise.

Constraints

All values in input are integers.

2 \leq N \leq 50

p is a permutation of {1,\ 2,\ ...,\ N}.

Input

Input is given from Standard Input in the following format:

N
p_1 p_2 ... p_N

Output

Print YES if you can sort p in ascending order in the way stated in the problem statement, and NO otherwise.

Sample Input 1

5
5 2 3 4 1

Sample Output 1

YES

You can sort p in ascending order by swapping p_1 and p_5.

Sample Input 2

5
2 4 3 5 1

Sample Output 2

NO

In this case, swapping any two elements does not sort p in ascending order.

Sample Input 3

7
1 2 3 4 5 6 7

Sample Output 3

YES

p is already sorted in ascending order, so no operation is needed.

Solution in JavaScript (node.js v5.12) (judge verdict: Wrong Answer)

"use strict"

function isSortable(args, sorted_args){
  let not_match_cnt = 0
  sorted_args.map((item, key)=>{
    if(sorted_args[key] != args[key]){
      not_match_cnt++
    }
  })
  if(not_match_cnt == 0 || not_match_cnt == 2){
    return true
  }else{
    return false
  }
}

const YES = 'YES'
const NO = 'NO'

const arg_str = require('fs').readFileSync('/dev/stdin', 'UTF-8')
const args_lines = arg_str.split('\n')
const n = args_lines[0]
const target = args_lines[1].split(' ')

if(target.length != n){
  console.log(NO)
  return
}

if(n < 2 ||  50 < n){
  console.log(NO)
  return
}

const args_asc = target.slice().sort((a,b)=>a-b)
const args_desc = target.slice().sort((a,b)=>b-a)

const is_sortable_asc = isSortable(target, args_asc)
const is_sortable_desc = isSortable(target, args_desc)

if(is_sortable_asc || is_sortable_desc){
  console.log(YES)
}else{
  console.log(NO)
}