package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

/*
del
add 12
del
add 10
add 9
del
del
del
add 10
del
add 1
add 8
add 20
add 1
add 11
add 2
del
del
del
del
*/
func main() {
	var cQueue = Constructor()
	input := bufio.NewScanner(os.Stdin)
	for input.Scan() {
		line := input.Text()
		if !strings.HasPrefix(line, "add ") && !strings.HasPrefix(line, "del") {
			continue
		}

		if strings.HasPrefix(line, "add ") {
			var digitStr = line[4:]
			var digit, _ = strconv.Atoi(digitStr)
			cQueue.AppendTail(digit)
			println("null")
			continue
		}
		if strings.HasPrefix(line, "del") {
			var digit = cQueue.DeleteHead()
			println(digit)
		}

		fmt.Println(cQueue.Stack1, "---", cQueue.Stack2)
	}
}

type CQueue struct {
	Stack1 []int
	Stack2 []int
}

func Constructor() CQueue {
	return CQueue{}
}

func (this *CQueue) AppendTail(value int) {
	this.Stack1 = append(this.Stack1, value)
}

func (this *CQueue) DeleteHead() int {
	if len(this.Stack1) == 0 {
		return -1
	}

	var value int

	this.Stack2 = append(this.Stack2, this.Stack1[0])
	value = this.Stack2[0]
	this.Stack1 = this.Stack1[1:]
	this.Stack2 = this.Stack2[1:]

	return value
}