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 Perl (5.26.1) (judge verdict: Accepted)

$n=<>;
@a=glob<>;
sub check{
	for(0..$n-2){
		if($a[$_]>$a[$_+1]){
			return 0;
		}
	}
	return 1;
}
if(check){
	print "YES";
	exit
}
for$i(0..$n-1){
	for$j($i+1..$n-1){
		($a[$i],$a[$j])=($a[$j],$a[$i]);
		if(check){
			print "YES";
			exit
		}
		($a[$i],$a[$j])=($a[$j],$a[$i]);
	}
}
print "NO";