main.py

# Authored by : gusdn3477
# Co-authored by : -
# Link : http://boj.kr/89f5e4e54afb441bbf218b5e68a4160d
import sys
from collections import deque

def input():
    return sys.stdin.readline().rstrip()

N = int(input())
queue = deque()
for i in range(N):
    command = input().split()
    if command[0] == "push":
        queue.append(command[1])
    elif command[0] == "pop":
        if queue:
            print(queue.popleft())
        else:
            print(-1)
    elif command[0] == "size":
        print(len(queue))
    elif command[0] == "empty":
        if not queue:
            print(1)
        else:
            print(0)
    elif command[0] == "front":
        if queue:
            print(queue[0])
        else:
            print(-1)
    elif command[0] == "back":
        if queue:
            print(queue[-1])
        else:
            print(-1)