print("Enter numbers one at a time.")
print("Type 'STOP' (in any case) when you are finished.\n")

total = 0

while True:
    user_input = input("Enter a number: ")
    
    if user_input.lower() == "stop":
        break
    
    try:
        number = float(user_input)
        total += number
    except ValueError:
        print("Invalid input. Please enter a number or STOP.")

print("Sum of entered numbers:", total)