VAT from sum | Python Fiddle

# -*- coding: utf_8 -*-

"""This program calculates how much money 
    you have to pay for gasoline, and calculates VAT (20% ("PDV" in Ukraine)).
    You have to enter how many liters you filled and 
    how much 1 liter costs.

This program was written for specific bookkeeper needs.

Formula:
    Sum = 1 litter cost * quantity + 20% * (1 litter cost * quantity)"""

def PodborCheck(litters, price):
    full_sum = litters * price
    sum_wo_vat = 0
    vat = 0
    x = 0
    while x < full_sum:
        sum_wo_vat += 0.01
        vat = sum_wo_vat * 0.2
        x = sum_wo_vat + vat

print(' ')
    print('Sum', round(full_sum, 2))
    print('VAT', round(vat, 2))
    print(' ')

def calc():
    z = 0
    lt = float(input("How many litters? "))
    pr = float(input("Cost by one? "))
    PodborCheck(lt, pr)
    try:
        z  = int(input("Press ENTER for exit. Press 1 and ENTER to continue. "))
        print(" ")
    except ValueError:
        return 0
    if z != 1:
        return 0
    else:
        calc()
calc()

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