# 2d table of users and passwords

users = [
    ["john", "password"],
    ["jane", "1234"],
    ["alice", "31234"],
    ["charlie", "1863"],
    ["david", "3958"],
]

def login():
    for i in range(3):
        username = input("Enter username: ").strip().lower()
        password = input("Enter password: ").strip()
        
        for user in users:
            if user[0] == username and user[1] == password:
                return True
                break
        
    return False

def main():
    log = login()
    
    if log:
        print("Login successful!")
    else:
        print("Invalid username or password.")

if __name__ == "__main__":
    main()