The automatic soft-drinks vending machine (SVM) is free and self checking every 10 minutes. After receiving the cash, the SVM waits for the user to select the desired drink. After the user makes a choice, the SVM checks whether the amount of cash entered by the customer is enough to buy the drink. If it is enough, the selected drink will be output; otherwise, it will wait for the user to continue to invest in cash. If the user does not make up the cash within one minute, the cash will be returned. During the purchase process, if the user presses the "Cancel" button, the cash will be returned. Task: draw a state chart diagram for the SVM.