#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int top=-1,size=5;
int arr[100];
void push(int num)
{
    if(top<size-1)
    {
    arr[++top]=num;
    }
}
void pop()
{
    if(top==-1)
    {
    printf("Stack Underflow\n");
    }
    else
    {
     top--;
    }
}
void peek()
{
    if(top==-1)
    printf("Stack Underflow\n");
    else
       printf("%d\n",arr[top]);
}
void display()
{
    if(top==-1)
    {
        printf("\n");
    }
    else{
    for(int i=0;i<=top;i++)
    {
        printf("%d ",arr[i]);
    }
    printf("\n");
    }
}
int main()
{
    int q,num;
    char cmd[20];
    scanf("%d",&q);
    while(q--)
    {
     scanf("%s",cmd);
    if(strcmp(cmd,"PUSH")==0)
    {
         scanf("%d",&num);
         push(num);
    }
    else if(strcmp(cmd,"POP")==0)
    {
    pop();
    }
    else if(strcmp(cmd,"PEEK")==0)
    {
        peek();
}
    else if(strcmp(cmd,"DISPLAY")==0)
    {
        display();
    }
    }
}