QUEUE_SIM.py

"""
Perform a sequence of operations over a queue, each element is an integer:
PUSH v: push a value v into the queue
POP: remove an element out of the queue and print this element to stdout (print NULL if the queue is empty)

Input:
      Each line contains a command (operration) of type
      PUSH  v
      POP
Output:
      Write the results of POP operations (each result is written in a line)
Example
Input:
      PUSH 1
      PUSH 2
      PUSH 3
      POP
      POP
      PUSH 4
      PUSH 5
      POP
      #
Output:
      1
      2
      3

Input:
      PUSH 1
      POP
      POP
      PUSH 4
      POP
      #
Output:
      1
      NULL
      4
"""

inp = "."
p = []
while(inp != "#"):
    inp = input()
    if inp=="#":
        break
    if "PUSH" in inp:
        p.append(inp[5:])
    else:
        if len(p) > 0:
            print(p[0])
            p.remove(p[0])
        else:
            print("NULL")