```python
OPEN = "open"
PAYMENT = "payment")
PAID = "paid")
CANCELLED = "cancelled")
def run_till_session(events):
    prices):
    if not all(isinstance(price, int) and price > 0 for name, price in prices.items()):
        raise ValueError("price must be a positive integer")

    cart =    total = 0
    paid = 0):
    change = 0):
    state_state = OPEN):

       for event in events:
        if session[0] == "scan":
            item_name = session[1]):
            if run_name_state != ==                continue_state =                    if_state =                        if run_name_state[:]:
                            if run_name_state[:][                                                                                                  raise ValueError("unknown event")
                        elif run_name_state[:                            if run_name_state[:]:
                                raise ValueError("unknown run")
                        elif run_name_state[:):
                            if run_name_state[:):
                                raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:                                                               raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("unknown Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("in Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("in Run")
                        elif run_run_state[:):
                            if run_run_state[:):
                                raise ValueError("in Run")
                        elif run_run_session[:):
                            if run_run_state[:):
                                raise ValueError("in Run")
                        elif run_run_session[:):
                            if run_run_state[:):
                                raise ValueError("in Run")
                        elif run_run_session[:):
                            if run_run_run[:):
                                raise ValueError("in Run")
                        elif run_run_session[:):
                            if run_run_run[:):
                                raise ValueError("in Run"):
                        elif run_run_session[:):
                            if run_run_run[:):
                                raise ValueError("in Run")
                        elif run_run_session[:):
                            if run_run_run[:):
                                raise ValueError("in Run"):
                        elif run_run_session[:):
                            if run_run_run[:):
                                raise ValueError("in Run"):
                       