백준(BOJ) 10845

#include <iostream>
#include <cstdio>
#include <queue>
#include <string.h>
using namespace std;
 
queue<int> q;
 
int main(void){
  int N;
  scanf("%d", &N);
  scanf("%*c");
  while(N--){
    char str[20];
    scanf("%s", str);
    if(strcmp(str, "push") == 0){
      int n;
      scanf("%d", &n);
      q.push(n);
      scanf("%*c");
    }
    else if(strcmp(str, "pop") == 0){
        if(q.empty()) printf("-1\n");
        else{
          printf("%d\n", q.front());
          q.pop();
        }
    }
    else if(strcmp(str, "size") == 0){
        printf("%d\n", q.size());
    }
    else if(strcmp(str, "empty") == 0){
        if(q.empty()) printf("1\n");
        else printf("0\n");
    }
    else if(strcmp(str, "front") == 0){
        if(q.empty()) printf("-1\n");
        else printf("%d\n", q.front());
    }
    else if(strcmp(str, "back") == 0){
      if(q.empty()) printf("-1\n");
      else printf("%d\n", q.back());
    }
  }
 
}