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.*;
import java.awt.geom.Point2D.Double;
import java.io.BufferedReader;
import java.io.InputStreamReader;

class Card {
    char    suit;
    int     value;
}

public class Main {
    private static int MAX = 100000;

    public static void main(String[] args) throws Exception {
            // 入力
            Card[]      A = new Card[MAX];
            Card[]      B = new Card[MAX];
            int     n;
//            Scanner sc = new Scanner(System.in);
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

//            n = Integer.parseInt(sc.next());
            n = Integer.parseInt(br.readLine());
            for (int i = 0; i < n; i++) {
                Card c = new Card();
/*                c.suit = sc.next().charAt(0);
                c.value = Integer.parseInt(sc.next());
*/
                String[] s = br.readLine().split(" ");
                c.suit = s[0].charAt(0);
                c.value = Integer.parseInt(s[1]);
                A[i] = c;

                Card c2 = new Card();
                c2.suit = c.suit;
                c2.value = c.value;
                B[i] = c2;
            }
//            sc.close();

            // クイックソート
            quickSort(A, 0, n - 1);
            // マージソート
            mergeSort(B, 0, n);

            // マージソートとクイックソートの結果を比べる
            String      s = "Stable";
            for (int i = 0; i < n; i++) {
                if (A[i].suit != B[i].suit) s = "Not stable";
            }

            // 出力
            System.out.println(s);
            for (int i = 0; i < n; i++) {
                System.out.println(A[i].suit + " " + A[i].value);
            }
    }

    static void mergeSort(Card[] A, int left, int right) {
        if (left + 1 < right) {
            int mid = (left + right) / 2;
            mergeSort(A, left, mid);
            mergeSort(A, mid, right);
            merge(A, left, mid, right);
        }
    }

    static Card[]       L = new Card[MAX / 2 + 2];
    static Card[]       R = new Card[MAX / 2 + 2];
    static final int    INFTY = 2000000000;
    static void merge(Card[] A, int left, int mid, int right) {
        int     n1 = mid - left;
        int     n2 = right - mid;
        for (int i = 0; i < n1; i++) {
            Card        c = new Card();
            c.suit = A[left + i].suit;
            c.value = A[left + i].value;
            L[i] = c;
        }
        for (int i = 0; i < n2; i++) {
            Card        c = new Card();
            c.suit = A[mid + i].suit;
            c.value = A[mid + i].value;
            R[i] = c;
        }

        Card    temp = new Card();
        temp.suit = 'D';
        temp.value = INFTY;
        L[n1] = temp;
        R[n2] = temp;

        int     i = 0;
        int     j = 0;
        for (int k = left; k < right; k++) {
            if (L[i].value <= R[j].value) {
                A[k] = L[i++];
            } else {
                A[k] = R[j++];
            }
        }
    }


    /**
     * 
     * @param A
     * @param n Aの長さ
     * @param p ソート対象の部分配列の開始位置
     * @param r ソート対象の部分配列の末尾
     */
    static void quickSort(Card[] A, int p, int r) {
        if (p < r) {
            int q = partition(A, p, r);
            quickSort(A, p, q - 1);
            quickSort(A, q + 1, r);
        }
    }

    static int partition(Card[] A, int p, int r) {
        int         x = A[r].value;       // 配列の末尾。判定の基準になる
        int         i = p - 1;      // A[r]以下を差す
        Card        temp;
        for (int j = p; j < r; j++) {
            if (A[j].value <= x) {
                i = i + 1;
                temp = A[i];
                A[i] = A[j];
                A[j] = temp;
            }
        }
        temp = A[i + 1];
        A[i + 1] = A[r];
        A[r] = temp;
        return i + 1;
    }
}