Python help - Game of Nim

Python novice here trying to trouble shoot my game of nim code. Basically the code removes stones 1, 2 or 3 stones until their is none left. I'm trying to prevent the user and AI from going into the negatives (if their is one stone left the AI/the user shouldn't be able remove two or three stones.) Here is my code so far:

import random
Stones = random.randint(15, 30)
User = 0
YourTurn = True

print("This is a game where players take turns taking stones from a pile of stones. The player who 
takes the last stone loses.")
print("The current stone count is:", Stones)

while True:
     while YourTurn == True and Stones > 0:
    User = int(input("How many stones do you want to remove?"))
    if User == 1:
        Stones -= 1
        print("You removed 1 stone! The current stone count is:", Stones)
        YourTurn = not True            
    elif User == 2:
        Stones -= 2
        print("You removed 2 stone! The current stone count is:", Stones)    
        YourTurn = not True                       
    elif User == 3:
        Stones -= 3
        YourTurn = not True
        print("You removed 3 stone! The current stone count is:", Stones)
    else:
        print("You can only remove a maximum of 3 stones.")

    while YourTurn == False and Stones > 0:
        AI = random.randint(1, 3)
        if AI == 1:
            Stones -= 1
            print("The A.I removed 1 stone! The current stone count is:", Stones)
            YourTurn = not False
        elif AI == 2:
            Stones -= 2
            print("The A.I removed 2 stone! The current stone count is:", Stones)
            YourTurn = not False
        elif AI == 3:
            Stones -= 3
            print("The A.I removed 3 stone! The current stone count is:", Stones)
            YourTurn = not False

if Stones <= 0:
    if YourTurn == True:
        print("The A.I took the last stone it lost. You won the game!")
        break
    elif YourTurn == False:
        print("You took the last stone you lost. The A.I won the game!")
        break

I have no idea how you would make the code not go into the negatives, the if and elif statements I had before were being ignored by the code. I would appreciate any help.