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 Card
  attr_reader :suit, :number

  def initialize(val)
    @suit = val[0]
    @number = val[1].to_i
  end

  def to_s
    "#{suit} #{number}"
  end

  def <=(card)
    number <= card.number
  end

  def ==(card)
    suit == card.suit && number == card.number
  end
end

def merge(a, left, mid, right)
  n1 = mid - left
  n2 = right - mid
  l = [] * n1
  r = [] * n2
  n1.times do |i|
    l << a[left + i]
  end
  n2.times do |i|
    r << a[mid + i]
  end
  li = 0
  ri = 0
  l << Card.new(["?", 0xffffffff.to_s])
  r << Card.new(["?", 0xffffffff.to_s])
  left.upto(right - 1) do |i|
    if l[li] <= r[ri]
      a[i] = l[li]
      li += 1
    else
      a[i] = r[ri]
      ri += 1
    end
  end
end

def _merge_sort(a, left, right)
  if left + 1 < right
    mid = (left + right) / 2
    _merge_sort(a, left, mid)
    _merge_sort(a, mid, right)
    merge(a, left, mid, right)
  end
  a
end

def merge_sort(a)
  _merge_sort(a, 0, a.size)
end

def swap(a, i, j)
  tmp = a[i]
  a[i] = a[j]
  a[j] = tmp
end

def partition(a, p, r)
  ans = p
  p.upto(r - 1) do |i|
    if a[i] <= a[r]
      swap(a, ans, i)
      ans += 1
    end
  end
  swap(a, ans, r)
  ans
end

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

def quicksort(a)
  _quicksort(a, 0, a.size - 1)
end

def stable?(bef, aft)
  merge_sort(bef) == aft
end

n = gets.chomp.to_i
a = []

n.times do
  a << Card.new(gets.chomp.split)
end

sorted = quicksort(a.dup)

puts stable?(a, sorted) ? 'Stable' : 'Not stable'
puts sorted.map(&:to_s).join("\n")