PROGRAMMING:Queue operation

Please implement a myqueue class to implement the queue length
The queue function void push (int x) is implemented;
Implementation of the queue function int pop();
Implementation of the queue length function int size();
###Input format:
Each input contains one test case. The first line of each test case is given a positive integer n (n < = 10 ^ 6), and the next N lines are given a number in each line to indicate an operation
1 x: insert x from the end of the team, 0 < = x < = 2 ^ 31-1.
2: Indicates that the first element of the team is out of the team.
3: Indicates the length of the queue.
###Output format:
For operation 2, if the queue is empty, output "invalid", otherwise, output the first element of the queue. For operation 3, output the queue length.
Each output item ends with a new line.
###Input example:
```in
five
three
two
1 100
three
two
```
###Output example:
```out
0
Invalid
one
one hundred
```






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