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