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)

#include<stdio.h>
#define MAX 100000

struct Card{
  char s;
  int v;
};

struct Card L[MAX], R[MAX];

void merge(struct Card [], int, int, int, int);

void m_sort(struct Card [], int , int, int);

int partition(struct Card [], int , int , int );

void quickSort(struct Card [], int  ,int , int );


int main(){
  int i, n, v;
  //クイックソートとマージソートを比べるために二つ配列を用意する
  struct Card M[MAX], Q[MAX];
  char S[10];
  int stable = 1;

  scanf("%d", &n);
  for( i = 0 ; i < n ; i++){
    scanf("%s %d", S, &v);
    M[i].s = Q[i].s = S[0];
    M[i].v = Q[i].v = v;
  }
  //マージソート
  m_sort(M, n, 0, n);
  //クイックソート
  quickSort(Q, n, 0, n-1);

  for( i = 0 ; i < n ; i++){
    //クイックソートとマージソートを比べる
    if( Q[i].s != M[i].s ) stable = 0;
  }

  if( stable == 1 ) printf("Stable\n");
  else printf("Not stable\n");
  for(i = 0 ; i < n ; i++){
    printf("%c %d\n", Q[i].s, Q[i].v);
  }
  return 0;
}

void merge(struct Card M[], int n, int left, int mid, int right){
  int i, j, k;
  int n1 = mid - left;
  int n2 = right - mid;
  //左部分のマージ
  for( i = 0 ; i < n1 ; i++ ){
    L[i] = M[left + i];
  }
  // 右部分のマージ
  for( i = 0 ; i < n2 ; i++ ){
    R[i] = M[mid + i];
  }
  L[n1].v = R[n2].v = 2000000000;
  i = j = 0;
  for( k = left ; k < right ; k++){
    //　L側とR側に振り分け
    if( L[i].v <= R[j].v ){
      M[k] = L[i++];
    }
    else{
      M[k] = R[j++];
    }
  }
}

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

// 要素を分割し、要素の標準（ピボット）となる要素の番号を返す。
int partition(struct Card A[], int n, int p, int r){
  int i, j;
  struct Card t, x;
  // t 一時避難用、x元カード保持
  x = A[r];
  i = p - 1;
  for( j = p ; j < r ; j++ ){
    if( A[j].v <= x.v ){
      i++;
      t = A[i];
      A[i] = A[j];
      A[j] = t;
    }
  }
  t = A[i+1];
  A[i+1] = A[r];
  A[r] = t;
  return i + 1;
}

void quickSort(struct Card Q[], int n ,int p, int r){
  int q;
  if( p < r ){
    // 要素の分割化
    q = partition(Q, n, p, r);
    // 分割した左部分
    quickSort(Q, n, p, q-1);
    // 分割した右部分
    quickSort(Q, n, q+1, r);
  }
}