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 main(input) {
  const lines = input.split('\n');
  lines.pop();
  const numberOfElements = parseInt(lines[0], 10);
  const array = lines[1].split(' ').map(x => {
    return parseInt(x, 10);
  });
  console.log(fn(array));
}

function fn(raw) {
  const keep = raw.slice();
  const sorted = raw.sort();
  let x = 0;
  let c = 0;
  while(x < keep.length && c <= 3) {
    if (keep[x] !== sorted[x]) {
      c++;
    }
    x++;
  }
  if (c < 3) {
    return 'YES';
  }
  return 'NO';
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));