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