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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"os"
	"strings"
	"strconv"
	"fmt"
)

var sc = bufio.NewScanner(os.Stdin)

func readLine() string {
	sc.Scan()
	return sc.Text()
}

func lineToInts(line string) []int {
	var array []int
	for _, s := range strings.Split(line, " ") {
		i, _ := strconv.Atoi(s)
		array = append(array, i)
	}
	return array
}

func main() {
	var n int
	fmt.Scan(&n)
	p := lineToInts(readLine())
	counter := 0
	for i := 0; i < len(p); i++ {
		if p[i] != i + 1 {
			counter++
			if counter > 2 {
				break
			}
		}
	}
	if counter > 2 {
		fmt.Println("NO")
	} else {
		fmt.Println("YES")
	}
}