#include<stdio.h>
#include<string.h>
#define max[100]

int stack[20];
int top=-1;
void push(int x,int size){
    if(top==top-1){
        printf("Stack Overflow");
    }
    stack[++top] = x;
}
void pop(){
    if(top==-1){
        printf("Stack Underflow");
        return;
    }
    top--;
}
void peek(){
    if(top==-1){
        printf("Stack Underflow");
    }
    printf("%d",stack[top]);
}
void display(){
    if(top==-1){
        printf("Stack Underflow");
    }
    for(int i=0; i<=top; i++){
        printf("%d ",stack[i]);
    }
}
int main(){
    int size;
    scanf("%d", &size);
    if(size<=0){
        printf("Invalid input");
    }
    char str[10];
    for(int i=0; i<=size; i++){
        scanf("%d",&str);
    }
    if(strcmp(str,"PUSH")==0){
        int x;
        scanf("%d",&x);
        push(x);
    }
    else if(strcmp(str,"POP")==0){
        pop();
    }
    else if(strcmp(str,"PEEK")==0){
        peek();
    }
    else{
        display();
    }
    return 0;
}