10845 큐

#include <stdio.h>
#include <string>
#include <iostream>
#include <queue>
 
using namespace std;
 
queue<int> q;
 
int main() {
    int t;
    scanf("%d", &t);
 
    while (t--) {
        string str;
        cin >> str;
        getchar();
                
        if (str == "push") {
            int n;
            scanf("%d", &n);
 
            q.push(n);
        }
        else if (str == "pop") {
            if (q.size() == 0) {
                printf("-1\n");
                continue;
            }
 
            int out = q.front();
            printf("%d\n", out);
 
            q.pop();
        }
        else if (str == "size") {
            printf("%d\n", q.size());
        }
        else if (str == "empty") {
            if (q.empty() == true) {
                printf("1\n");
            }
            else {
                printf("0\n");
            }
        }
        else if (str == "front") {
            if (q.empty() == true) {
                printf("-1\n");
            }
            else {
                printf("%d\n",q.front());
            }
        }
        else if (str == "back") {
            if (q.empty() == true) {
                printf("-1\n");
            }
            else {
                printf("%d\n",q.back());
            }
        }
    }
}