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 Ruby (2.3.3) (judge verdict: Accepted)

N = gets.chomp.to_i
p = gets.chomp.split(" ").map(&:to_i)

def makeOrder()
  ary = []
  ary.fill(0, N) {|i| i+1}
end

class Array
  def diff(ary)
    retAry = []
    self.each_index{ |i|
      if self[i] != ary[i]
        retAry.push(self[i])
      end
    }
    retAry
  end
end

diffAry = p.diff(makeOrder())

if diffAry.empty?
  puts "YES"
elsif diffAry.length == 2 && p.index(diffAry[0])+1 == diffAry[1]
  puts "YES"
else
  puts "NO"
end