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"
	"fmt"
	"os"
	"strconv"
)

func main() {
	n := getInt()
	ps := getIntSlice(n)

	cnt := 0
	for i, p := range ps {
		if p != i+1 {
			cnt++
		}
	}

	ans := "YES"
	if cnt > 2 {
		ans = "NO"
	}
	fmt.Println(ans)
}

// -----------------------------------------

var scanner = wordScanner()

func wordScanner() *bufio.Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	return sc
}

func getInt() int {
	scanner.Scan()
	i, err := strconv.Atoi(scanner.Text())
	if err != nil {
		panic(err)
	}
	return i
}

func getIntSlice(n int) []int {
	is := make([]int, n)
	for i := range is {
		is[i] = getInt()
	}
	return is
}

func getString() string {
	scanner.Scan()
	s := scanner.Text()
	return s
}