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 C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ALDS1_6_C
{
    class Program
    {
        private static int targetCount;
        private static Card[] targetArray;
        private static Card[] targetArray2;

        static void Main(string[] args)
        {
            Program.targetCount = int.Parse(Console.ReadLine());
            Program.targetArray = new Card[Program.targetCount];
            Program.targetArray2 = new Card[Program.targetCount];

            for (int i = 0; i < Program.targetCount; i++)
            {
                string[] tmpArry = Console.ReadLine()
                                          .Split(' ');
                targetArray[i] = new Card(tmpArry[0], int.Parse(tmpArry[1]));
            }

            Program.targetArray.CopyTo(Program.targetArray2, 0);

            Program.QuickSort(0, Program.targetCount - 1);
            Program.MergeSort(0, Program.targetCount - 1);

            for (int i = 0; i < Program.targetArray.Length; i++)
            {
                if (!Program.targetArray[i].Equals(Program.targetArray2[i]))
                {
                    Console.WriteLine("Not stable");
                    break;
                }
                if (i == Program.targetArray.Length - 1)
                {
                    Console.WriteLine("Stable");
                }
            }

            foreach (var item in Program.targetArray)
            {
                Console.WriteLine(item.ToString());
            }
            Console.ReadLine();
        }

        private static int Partition(int leftInd, int rightInd)
        {
            Card partition = Program.targetArray[rightInd];
            int tmpInd = leftInd - 1;

            for (int i = leftInd; i < rightInd; i++)
            {
                //if (Program.targetArray[i] <= partition)
                if (partition.IsLarger(Program.targetArray[i]))
                {
                    tmpInd++;
                    Card tmpCard = Program.targetArray[i];
                    Program.targetArray[i] = Program.targetArray[tmpInd];
                    Program.targetArray[tmpInd] = tmpCard;
                }
            }
            tmpInd++;
            Program.targetArray[rightInd] = Program.targetArray[tmpInd];
            Program.targetArray[tmpInd] = partition;
            return tmpInd;
        }

        private static void QuickSort(int leftInd, int rightInd)
        {
            if (leftInd < rightInd)
            {
                int partitionInd = Program.Partition(leftInd, rightInd);
                Program.QuickSort(leftInd, partitionInd - 1);
                Program.QuickSort(partitionInd + 1, rightInd);
            }
            return;
        }

        private static void Merge(int leftInd, int midInd, int rightInd)
        {
            Card[] leftArry = new Card[midInd - leftInd + 1];
            Card[] rightArry = new Card[rightInd - midInd];

            for (int i = 0; i < leftArry.Length; i++)
            {
                leftArry[i] = Program.targetArray2[leftInd + i];
            }

            for (int i = 0; i < rightArry.Length; i++)
            {
                rightArry[i] = Program.targetArray2[midInd + 1 + i];
            }

            for (int l = 0, r = 0, k = leftInd; k <= rightInd; k++)
            {
                if (l < leftArry.Length && r >= rightArry.Length || l < leftArry.Length && r < rightArry.Length && rightArry[r].IsLarger(leftArry[l]))
                {
                    Program.targetArray2[k] = leftArry[l];
                    l++;
                }
                else
                {
                    Program.targetArray2[k] = rightArry[r];
                    r++;
                }
            }
        }

        private static void MergeSort(int leftInd, int rightInd)
        {
            if (leftInd < rightInd)
            {
                int midInd = (leftInd + rightInd) / 2;
                Program.MergeSort(leftInd, midInd);
                Program.MergeSort(midInd + 1, rightInd);
                Program.Merge(leftInd, midInd, rightInd);
            }
            return;
        }
    }

    class Card
    {
        private string suit;
        private int num;

        public Card(string suit, int num)
        {
            this.suit = suit;
            this.num = num;
        }

        public bool IsLarger(Card targetCard)
        {
            return targetCard.num <= this.num;
        }

        public override bool Equals(object obj)
        {
            if (obj == null || this.GetType() != obj.GetType())
            {
                return false;
            }

            Card targetCard = (Card)obj;

            return this.suit == targetCard.suit && this.num == targetCard.num;
        }

        public override string ToString()
        {
            return string.Format("{0} {1}", this.suit, this.num);
        }
    }
}