#include<stdio.h>
#define Max 100000
#define SENT 2000000000

typedef struct{
  char suit;
  int value;
}Card;
void merge(Card A[],int n,int left,int mid,int right);
void mergesort(Card A[],int n,int left,int right);
int partition(Card *A,int n,int p,int r);
void quickSort(Card *A,int n,int p,int r);
Card Left[Max/2+2],Right[Max/2+2];
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].suit=S[0];
    B[i].suit=S[0];
    A[i].value=v;
    B[i].value=v;
  }
  mergesort(A,n,0,n);
  quickSort(B,n,0,n-1);
  for(i=0;i<n;i++){
    if(A[i].suit!=B[i].suit)stable=0;
  }
  if(stable)printf("stable\n");
  else printf("Not stable\n");
  for(i=0;i<n;i++){
    printf("%c %d\n",B[i].suit,B[i].value);
  }
  return 0;
}
void merge(Card A[],int n,int left,int mid,int right){
  int A1=mid-left;
  int A2=right-mid;
  int i,j,m;
  for(i=0;i<A1;i++)Left[i] = A[left+i];
  for(i=0;i<A2;i++)Right[i]=A[mid+i];
  Left[A1].value=SENT;
  Right[A2].value=SENT;
  i=0;
  j=0;
  for(m=left;m<right;m++){
    if(Left[i].value<=Right[j].value){
      A[m]=Left[i++];
    }else{
      A[m]=Right[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 x,tmp;
  x=A[r];
  i=p-1;
  for(j=p;j<r;j++){
    if(A[j].value<=x.value){
      i++;
      tmp=A[i];
      A[i]=A[j];
      A[j]=tmp;
    }
  }
  tmp=A[i+1];
  A[i+1]=A[r];
  A[r]=tmp;
  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);
  }
}