#include<stdio.h>
#define MAX 100000
#define SENTINEL 2000000000

struct Card{
  char suit;
  int value;
};

struct Card L[MAX / 2 + 2],R[MAX / 2+2];

voidmerge(struct Card A[], int n,int left,int mid inttight){
  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(struct 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(struct Card A[], int n, int p,int r){
  int i,j;
  struct 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(struct 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;
  struct 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 = B[i].suit = 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].suit != B[i].suit) 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].suit,B[i].value);
  }
  
  return 0;
}