#include <stdio.h>
#define MAX 100000
#define SENTINEL 2000000000
 
typedef struct{
  char name;
  int value;
}Card;



Card L[MAX / 2 + 2], R[MAX / 2 + 2];
 
void merge(Card A[],int n,int left,int mid,int right) {
  int i, j, k;
  int n1 = mid - left;
  int n2 = right - mid;
   
  for(i = 0; i < n1; i++) 
    L[i] = A[left + i];
   
  for(i = 0; i < n2; i++) 
    R[i] = A[mid + i];
   
  L[n1].value = R[n2].value = SENTINEL;
  i = j = 0;
   
  for(k = left; k < right; k++) {
    if(L[i].value <= R[j].value) {
      A[k] = L[i++];
    } else {
      A[k] = R[j++];
    }
  }
}
 
void mergeSort(Card A[], int n, int left, int right) {
   
  int mid;
   
  if(left + 1 < right) {
    mid = (left + right) / 2;
    mergeSort(A, n, left, mid);
    mergeSort(A, n, mid, right);
    merge(A, n, left, mid, right);
  }
}
 
int partition(Card A[], int n, int p, int r) {
   
  int i, j;
  Card t, x;
  x = A[r];
  i = p - 1;
   
  for(j = p; j < r; j++) {
    if(A[j].value <= x.value) {
      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(Card A[], int n, int p, int r) {
   
  int q;
   
  if(p < r) {
    q = partition(A, n, p, r);
    quickSort(A, n, p, q - 1);
    quickSort(A, n, q + 1, r);
  }
}
 
int main(){
  int n,i,v;
  Card A[MAX],B[MAX];
  char S[10];
  int stable = 1;
   
  scanf("%d", &n);
  for(i = 0; i < n; i++) {
    scanf("%s %d", S, &v);
    A[i].name = B[i].name = S[0];
    A[i].value = B[i].value = v;
  }
   
   
   
  mergeSort(A, n, 0, n);
  quickSort(B, n, 0, n - 1);
   
  for(i = 0; i < n; i++) {
    if(A[i].name != B[i].name) 
      stable = 0;
  }
   
   
   
  if(stable == 1) printf("Stable\n");
  else printf("Not stable\n");
   
   
   
  for(i = 0; i < n; i++) {
    printf("%c %d\n", B[i].name,B[i].name);
  }
   
  return 0;
}