#include<stdio.h>
#include<string.h>
#define max 100
int stack[max];
int top=-1;
int main(){
    int q;
    scanf("%d",&q);
    if(q<0){
        printf("Invalid input");
        return 0;
    }
    for(int i=0;i<q;i++){
        char command[20];
        scanf("%s",command);
    if(strcmp(command,"PUSH")==0){
        int x;
        scanf("%d",&x);
        if(top<MAX-1){
            stack[++top]=x;
        }
    }
    else if(strcmp(command,"PEEK")==0){
        if(top==-1){
            printf("Stack Underflow\n");
        }else{
            printf("%d\n",stack[top]);
        }
    }
    else if(strcmp(command,"POP")==0){
        if(top==-1){
            printf("Stack Underflow\n");
        }else{
              top--;
        }
    }
    else if(strcmp(command,"DISPLAY")==0){
        if(top==-1){
            printf("Stack Underflow");
        }else{
            for(int j=0;j<=top;j++){
                printf("%d ",stack[j]);
            }
            printf("\n");
        }
    }
    }
    return 0;
}