Redirecting the user input when entering invalid value [duplicate]

This question already has an answer here:

• Asking the user for input until they give a valid response 14 answers

Hello and thank you for taking the time out of your day to look at my question. I'm working on an assignment that will calculate the total of a number of bottles from user input. I have the code mostly working properly. But, we are also supposed to have the user redirected if they input a negative or alphabetic number. I've tried implementing some if statements and other conditional statements but still haven't quite got what I'm looking for. I think the portion of the code I've provided is where the user will be redirected if they input an invalid input. I can be provided further clarifications if needed. As this is my first time posting on StackOverflow. Even just a general hint would beneficial :)

def Bottles2(bottles, bottles_each_day, counter): while counter <= 7:

    bottles_each_day = input("enter total bottles returned for the seven days ")
    bottles_each_day = (bottles_each_day)
    bottles += int(float(bottles_each_day))
    counter = (counter + 1)

return bottles