Ticket program accepts negative values for requested tickets

TICKET_PRICE = 10
SERVICE_CHARGE = 2.25

tickets_remaining = 100  

def calcPrice(num_tickets):
    return (requested_tickets * TICKET_PRICE) + SERVICE_CHARGE 

while tickets_remaining >= 1:
    print("There are {} tickets remaining.".format(tickets_remaining))
    name = input("what is your name? ")
    requested_tickets = input("how many tickets do you need? ")
    try:
        requested_tickets = int(requested_tickets)
        if requested_tickets > tickets_remaining or requested_tickets < 0:
          raise ValueError("invalid number or too many tickets requested, Please try again")
    except ValueError as err:
        print("{}.".format(err))
    else:
        amount_due = calcPrice(requested_tickets)
        print("Your total for {} tickets is ${} ".format(requested_tickets, amount_due))
        should_proceed = input("Confirm purchase? Y/N ")
        if should_proceed.lower() == "y":
            print("SOLD!")
            tickets_remaining -= requested_tickets
        else: 
            print("Thank you anyways, {}".format(name))
print("Sorry all of the tickets are sold out")