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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;

public class Main {
	
	public static class Card implements Comparable<Card> {
		char suite;
		int value;
		
		public Card(char suite, int value) {
			super();
			this.suite = suite;
			this.value = value;
		}

		@Override
		public int compareTo(Card arg0) {
			return this.value - arg0.value;
		}
		
		@Override
		public String toString(){
			return this.suite + " " + this.value;
		}

		@Override
		public int hashCode() {
			final int prime = 31;
			int result = 1;
			result = prime * result + suite;
			result = prime * result + value;
			return result;
		}

		@Override
		public boolean equals(Object obj) {
			if (this == obj)
				return true;
			if (obj == null)
				return false;
			if (getClass() != obj.getClass())
				return false;
			Card other = (Card) obj;
			if (suite != other.suite)
				return false;
			if (value != other.value)
				return false;
			return true;
		}
	}
	
	public static int partition(Card[] A, int p, int r){
		final int x = A[r].value;
		
		int i = p - 1;
		for(int j = p; j < r; j++){
			if(A[j].value <= x){
				i++;
				
				Card tmp = A[i];
				A[i] = A[j];
				A[j] = tmp;
			}
		}
		
		Card tmp = A[i + 1];
		A[i + 1] = A[r];
		A[r] = tmp;
		
		return i + 1;
	}
	
	public static void quickSort(Card[] A, int p, int r){
		if(p < r){
			final int q = partition(A, p, r);
			quickSort(A, p, q - 1);
			quickSort(A, q + 1, r);
		}
	}
	
	public static void mergeSort(final Card[] A, final int left, final int right){ //[left, right)        
        if(left + 1 < right){
            final int mid = (left + right) / 2;
             
            mergeSort(A, left, mid);
            mergeSort(A, mid, right);
             
            final int l_size = mid - left;
            final int r_size = right - mid;
            final int size = l_size + r_size;
            Card[] ls = new Card[l_size];
            for(int i = 0; i < l_size; i++){
                ls[i] = A[left + i];
            }
            Card[] rs = new Card[r_size];
            for(int i = 0; i < r_size; i++){
                rs[i] = A[mid + i];
            }
             
            int l_pos = 0, r_pos = 0;
            int count = 0;
            while(count < size){
                if(l_pos == l_size){
                	A[left+count] = rs[r_pos];
                	r_pos++;
                }else if(r_pos == r_size){
                	A[left+count] = ls[l_pos];
                	l_pos++;
                }else if(ls[l_pos].compareTo(rs[r_pos]) <= 0){
                    A[left + count] = ls[l_pos];
                    l_pos++;
                }else{
                    A[left + count] = rs[r_pos];
                    r_pos++;
                }
                count++;
            }
        }
    }
	
	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		
		final int n = sc.nextInt();
		Card[] array = new Card[n];
		Card[] stable = new Card[n];
		for(int i = 0; i < n; i++){
			final char suite = sc.next().charAt(0);
			final int value = sc.nextInt();
			
			array[i] = new Card(suite, value);
			stable[i] = new Card(suite, value);
		}
		
		quickSort(array, 0, n - 1);
		mergeSort(stable, 0, n);
		
		boolean same = true;
		for(int i = 0; i < n; i++){
			if(!array[i].equals(stable[i])){
				same = false;
				break;
			}
		}
		
		System.out.println(same ? "Stable" : "Not stable");
		for(int i = 0; i < n; i++){
			System.out.println(array[i]);
		}
	}
	
	public static class Scanner {
	    private BufferedReader br;
	    private StringTokenizer tok;

	    public Scanner(InputStream is) throws IOException {
	        br = new BufferedReader(new InputStreamReader(is));
	    }

	    private void getLine() throws IOException {
	        while (!hasNext()) { tok = new StringTokenizer(br.readLine()); }
	    }

	    private boolean hasNext() {
	        return tok != null && tok.hasMoreTokens();
	    }

	    public String next() throws IOException {
	        getLine(); return tok.nextToken();
	    }

	    public int nextInt() throws IOException {
	        return Integer.parseInt(next());
	    }
	    
	    public long nextLong() throws IOException {
	    	return Long.parseLong(next());
	    }
	    
	    public void close() throws IOException {
	        br.close();
	    }
	}

}