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 JAVA (judge verdict: Accepted)

import java.util.Scanner;

/**
 * Created by zhangrunfeng on 2/17/20
 */
public class Main {

    public int N;
    public Card[] mergeSortArr;
    public Card[] quickSortArr;

    private Card[] tmpArr;

    static class Card {
        public char suit;
        public int value;

        public Card(char suit, int value) {
            this.suit = suit;
            this.value = value;
        }
    }

    public Main(Scanner sc) {
        N = sc.nextInt();
        mergeSortArr = new Card[N];
        quickSortArr = new Card[N];
        for (int i = 0; i < N; i++) {
            char suit = sc.next().charAt(0);
            int value = sc.nextInt();
            mergeSortArr[i] = new Card(suit, value);
            quickSortArr[i] = mergeSortArr[i];
        }
        tmpArr = new Card[N];
    }

    public void mergeSort(Card[] arr, int startIx, int endIx) {
        if (endIx - startIx <= 1) return;

        int midIx = startIx + (endIx - startIx) / 2;
        mergeSort(arr, startIx, midIx);
        mergeSort(arr, midIx, endIx);

        // merge section
        for (int i = startIx; i < endIx; i++) {
            tmpArr[i] = arr[i];
        }

        int ix1 = startIx, ix2 = midIx, ix = startIx;
        while (ix1 < midIx && ix2 < endIx) {
            if (tmpArr[ix1].value <= tmpArr[ix2].value) {
                arr[ix] = tmpArr[ix1];
                ix1++;
            } else {
                arr[ix] = tmpArr[ix2];
                ix2++;
            }
            ix++;
        }
        while (ix1 < midIx) {
            arr[ix] = tmpArr[ix1];
            ix++;
            ix1++;
        }
        while (ix2 < endIx) {
            arr[ix] = tmpArr[ix2];
            ix++;
            ix2++;
        }
    }

    // [startIx, endIx)
    public int partition(Card[] arr, int startIx, int endIx) {
        int parIx = startIx - 1;
        int pivotVal = arr[endIx - 1].value;
        for (int ix = startIx; ix < endIx; ix++) {
            if (arr[ix].value <= pivotVal) {
                parIx++;
                Card tmp = arr[ix];
                arr[ix] = arr[parIx];
                arr[parIx] = tmp;
            }
        }
        return parIx;
    }

    public void quickSort(Card[] arr, int startIx, int endIx) {
        if (endIx - startIx <= 1) return;
        int parIx = partition(arr, startIx, endIx);
        quickSort(arr, startIx, parIx);
        quickSort(arr, parIx+1, endIx);
    }

    public void printArr(Card[] arr) {
        for (Card card : arr) {
            System.out.println(card.suit + " " + String.valueOf(card.value));
        }
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Main m = new Main(sc);
        m.mergeSort(m.mergeSortArr, 0, m.N);
        m.quickSort(m.quickSortArr, 0, m.N);

        boolean flag = true;
        for (int i = 0; i < m.N; i++) {
            if (m.quickSortArr[i] != m.mergeSortArr[i]) {
                flag = false;
                break;
            }
        }

        if (flag) {
            System.out.println("Stable");
        } else {
            System.out.println("Not stable");
        }
        m.printArr(m.quickSortArr);
    }
}