#include <stdio.h>
#include <stdlib.h>

int* queue;
int front = 0;
int rear = 0;
int MAX_SIZE;

int is_empty(){
    if(front == rear){
        return 1;
    }
    else{
        return 0;
    }
}

int is_full(){
    if(front == (rear + 1) % MAX_SIZE){
        return 1;
    }
    else{
        return 0;
    }
}

void enqueue(int e){
    if(is_full()){
        printf("overflow\n");
        exit(0);
    }
    else{
        rear = (rear+1)%MAX_SIZE;
        queue[rear]=e;
    }
}

int dequeue(){
    if(is_empty()){
        printf("underflow\n");
        exit(0);
    }
    else{
        front = (front + 1)%MAX_SIZE;
        return queue[front];
    }
}

int peek(){
    if(is_empty()){
        printf("underflow\n");
        exit(0);
    }
    else{
        return queue[(front+1)%MAX_SIZE];
    }
}

int main(void){

    int N;
    scanf("%d", &N);

    MAX_SIZE = N+1;
    queue = (int*)malloc(sizeof(int) * MAX_SIZE);

    int a;
    while(1){
        scanf("%d", &a);

        if(a == -1){
            printf("%d\n", dequeue());
        }
        else if(a == -2){
            printf("%d\n", peek());
        }
        else if(a == 0){
            free(queue);
            break;
        }
        else if(a > 0){
            enqueue(a);
        }
    }
    return 0;
}