#include<stdio.h>
#include<string.h>

#define MAX_SIZE 100


int main(){
    int n;
    if(scanf("%d", &n) != 1)
    return 0;
    if(n<0) {
        printf("Invalid input");
        return 0;
    }
    int stack[MAX_SIZE];
    int top=-1;
    for (int i=0;i<n;i++){
        char cmd[10];
        scanf("%s",cmd);
        if(strcmp(cmd,"PUSH")==0) {
            int x;
            scanf("%d",&x);
            if (top<MAX_SIZE-1){
                stark[++top] =x;
            }
        }else if (strcmp(cmd,"POP") ==0) {
            if(top == -1){
                printf("stack Underflow\n");
            } else {
                top--;
            }
        }
        else if(strcmp(cmd,"PEEK")==0) {
            if(top == -1) {
                printf("stack Underflow\n");
            } else {
                printf("%d\n",stack[top]);
            }
        } else if(strcmp(cmd,"DISPLAY") == 0){
            if(top == -1) {
        }
        else {
            for(int j=0;j<= top;j++) {
                printf("%d ",stack[j]);
            }
        }
        printf("\n")
    }
}
return 0;
}