Write a computer program that could be used to track users' activities. Lab Number Computer Station Numbers 1 1-3 2 1-4 3 1-5 4 1-6  You run four computer labs. Each lab contains computer stations that are numbered as the above table.  There are two types of users: student and staff. Each user has a unique ID number. The student ID starts with three characters (for example, SWE or DMT), and is followed by three digits (like, 001). The staff ID only contains digits (for example: 2023007).  Whenever a user logs in, the user’s ID, lab number, the computer station number and login date are transmitted to your system. For example, if user SWE001 logs into station 2 in lab 3 in 01 Dec, 2022, then your system receives (+ SWE001 2 3 1/12/2022) as input data. Similarly, when a user SWE001 logs off in 01 Jan, 2023, then your system receives receives (- SWE001 1/1/ 2023). Please use = for end of input.  When a user logs in or logs off successfully, then display the status of stations in labs. When a user logs off a station successfully, display student id of the user, and the number of days he/she logged into the station.  When a user logs off, we calculate the price for PC use. For student, we charge 0 RMB if the number of days is not greater than 14, and 1 RMB per day for the part over 14 days. For staff, we charge 2 RMB per day if the number of days is not greater than 30, and 4 RMB per day for the part over 30 days.  If a user who is already logged into a computer attempts to log into a second computer, display "invalid login". If a user attempts to log into a computer which is already occupied, display "invalid login". If a user who is not included in the database attempts to log off, display "invalid logoff".

Here is a possible implementation of the program in Python:

import datetime

# initialize the status of all stations to False
status = [[False for j in range(4)] for i in range(5)]

# initialize the dictionary of users
users = {}

# define the function to check if a user is already logged in
def is_user_logged_in(user_id):
    for i in range(5):
        for j in range(4):
            if status[i][j] and users[(i+1, j+1)] == user_id:
                return True
    return False

# define the function to log in a user
def log_in(user_id, lab_num, station_num, login_date):
    if is_user_logged_in(user_id):
        print("invalid login")
    elif status[lab_num-1][station_num-1]:
        print("invalid login")
    else:
        status[lab_num-1][station_num-1] = True
        users[(lab_num, station_num)] = user_id
        print("user", user_id, "logged in at lab", lab_num, "station", station_num)
        print("status:", status)
        
# define the function to log off a user
def log_off(user_id, logoff_date):
    found = False
    for i in range(5):
        for j in range(4):
            if status[i][j] and users[(i+1, j+1)] == user_id:
                status[i][j] = False
                days = (logoff_date - datetime.date.today()).days
                print("user", user_id, "logged off at lab", i+1, "station", j+1)
                print("number of days logged in:", days)
                found = True
                break
        if found:
            break
    else:
        print("invalid logoff")
        return
    
    if user_id.startswith("S"):
        if days <= 14:
            price = 0
        else:
            price = (days - 14) * 1
    else:
        if days <= 30:
            price = 0
        else:
            price = (days - 30) * 4 + 30 * 2
    print("price:", price, "RMB")
    
# example usage
log_in("SWE001", 3, 2, datetime.date(2022, 12, 1))
log_in("SWE001", 3, 3, datetime.date(2022, 12, 1)) # expected output: invalid login
log_in("SWE002", 3, 2, datetime.date(2022, 12, 1))
log_off("SWE001", datetime.date(2023, 1, 1))
log_off("SWE003", datetime.date(2023, 1, 1)) # expected output: invalid logoff

Note that this is just one possible implementation, and there may be other ways to structure the program.