큐

#include <algorithm>
#include <iostream>
#include <stdio.h>
#include <vector>
#include <map>
#include <stack>
#include <queue>
using namespace std;



int main() {
	//freopen("input.txt", "rt", stdin);
	queue<int> q;
	int n;
	scanf("%d", &n);
	string s;
	for (int i = 0; i < n; i++) {
		cin >> s;
		if (s == "push") {
			int num;
			cin >> num;
			q.push(num);
		}
		else if (s == "front") {
			if (q.empty()) {
				printf("-1\n");
			}
			else {
				printf("%d\n", q.front());
			}
		}
		else if (s == "back") {
			if (q.empty()) {
				printf("-1\n");
			}
			else {
				printf("%d\n", q.back());
			}
		}
		else if (s == "pop") {
			if (q.empty()) {
				printf("-1\n");
			}
			else {
				printf("%d\n", q.front());
				q.pop();
			}
		}
		else if (s == "size") {
			printf("%d\n", q.size());
		}
		else if (s == "empty") {
			if (q.empty()) {
				printf("1\n");
			}
			else {
				printf("0\n");
			}
		}
	}
	

	return 0;
}