#include<stdio.h>
#include<stdlib.h>
typedef struct Node{
    int id;
    int ar;
    struct Node *next;
}node;

node *front=NULL,*rear=NULL;
void enqueue(int v,int t){
    node *newnode=(node*)malloc(sizeof(node));
    newnode->id=v;
    newnode->ar=t;
    newnode->next=NULL;
    if(front==NULL){
        front=rear=newnode;
    }
    else{
        rear->next=newnode;
        rear=newnode;
    }
}
void dequeue(){
    if(front==NULL){
        printf("Oueue is empty");
    }
    while(front!=NULL){
        printf("%d",front->id);
        front=front->next;
    }
}
int main(){
    int size;
    scanf("%d",&size);
    if(size<=0){
        printf("Invalid input");
        retrun 0;
    }
    for(int i=0;i<size;i++){
        int x,y;
        if(scanf("%d %d",&x,&y)!=2){
            printf("Invalid input");
            return 0;
        }
            if(x<0||y=0){
                printf("Invalid input");
                return 0;
            }
            enqueue(x,y);
        }
        dequeue();
    
    }
}