#include<stdio.h>
#include<string.h>
#define MAX 100
int main(){
    int q;
    scanf("%d",&q);
    if(q<0){
        printf("Invalid input");
        return 0;
    }
    int stack[MAX];
    int top=-1;
    char cmd[10];
    int value;
    for(int i=0;i<q;i++){
        scanf("%s",cmd);
        if(strcmp(cmd,"PUSH")==0){
            scanf("%d",&value);
            if(top<MAX-1){
                stack[++top]=value;
            }
        }
                else if(strcmp(cmd,"POP")==0)
                if(top==-1){
                    printf("Stack Underflow");
                }
                else{
                    top--;
                }
            }else if(strcmp(cmd,"PEEK")==0){
                if(top==-1){
                    printf("Stack Underflow");
                }
            }else{
                printf("%d\n",stack[top]);
            }
        }else if(strcmp(cmd,"DISPLAY")==0){
            if(top==-1){
                printf("Stack Underflow");
            }else{
                for(int j=0;j<=top;j++)
                {
                    printf("%d ",stack[j]);
                }
                printf("\n");
            }
            }
        }
    }
    return 0;
}