Problem:
Quick Sort

Let's arrange a deck of cards. Your task is to sort totally n cards. A card consists of a part of a suit (S, H, C or D) and an number. Write a program which sorts such cards based on the following pseudocode:

Partition(A, p, r)
1 x = A[r]
2 i = p-1
3 for j = p to r-1
4 do if A[j] <= x
5 then i = i+1
6 exchange A[i] and A[j]
7 exchange A[i+1] and A[r]
8 return i+1

Quicksort(A, p, r)
1 if p < r
2 then q = Partition(A, p, r)
3 run Quicksort(A, p, q-1)
4 run Quicksort(A, q+1, r)

Here, A is an array which represents a deck of cards and comparison operations are performed based on the numbers.

Your program should also report the stability of the output for the given input (instance). Here, 'stability of the output' means that: cards with the same value appear in the output in the same order as they do in the input (instance).

Input

The first line contains an integer n, the number of cards.

n cards are given in the following lines. Each card is given in a line and represented by a pair of a character and an integer separated by a single space.

Output

In the first line, print the stability ("Stable" or "Not stable") of this output.

In the following lines, print the arranged cards in the same manner of that of the input.

Constraints

1 ≤ n ≤ 100,000

1 ≤ the number of a card ≤ 109

There are no identical card in the input

Sample Input 1

6
D 3
H 2
D 1
S 3
D 2
C 1

Sample Output 1

Not stable
D 1
C 1
D 2
H 2
D 3
S 3

Sample Input 2

2
S 1
H 1

Sample Output 2

Stable
S 1
H 1

Solution in Ruby (judge verdict: Accepted)

class QuickSort

  class Card
    attr_accessor :mark, :number

    def initialize(mark, number)
      @mark = mark
      @number = number
    end

  end

  # Example:
  # a ::= [ "D 3", "H 2", "D 1" ]
  def initialize(a)
    @cards = []
    a.each do |pair|
      mark, number = pair.split
      @cards << Card.new(mark, number.to_i)
    end
    @cards_ini = @cards.dup
  end

  def solve(p, r)
    if p < r
      q = partition(p, r)
      solve(p, q-1)
      solve(q+1, r)
    end
  end

  def dump
    puts stable ? "Stable" : "Not stable"
    @cards.each do |card|
      puts "#{card.mark} #{card.number}"
    end
  end

  private

    def partition(p, r)
      x = @cards[r].number
      i = p - 1
      (p..r-1).each do |j|
        if @cards[j].number <= x
          i += 1
          @cards[i], @cards[j] = @cards[j], @cards[i]
        end
      end
      @cards[i+1], @cards[r] = @cards[r], @cards[i+1]
      return i+1
    end

    def stable
      cards_ini = {}
      cards = {}
      @cards_ini.each do |c|
         cards_ini[c.number] ||= []
         cards_ini[c.number] << c.mark
      end
      @cards.each do |c|
         cards[c.number] ||= []
         cards[c.number] << c.mark
      end
      cards_ini.each do |key, value|
        return false if value != cards[key]
      end
      return true
    end
end

n = gets.to_i
cards = (1..n).collect {|i| gets }

qs = QuickSort.new cards
qs.solve(0, n-1)
qs.dump