Coding a change calculator

from decimal import *          #I use the decimal format to ensure that the money is handled properly
getcontext().prec = 2          #This tells the program how many decimal places to put on the end of things


out20P=0          #Setting all my variables up
out10P=0
out5P=0
out2P=0
out1P=0
out50p=0
out20p=0
out10p=0
out5p=0
out2p=0
out1p=0
left=0
bill=1
payment=0


while payment<bill:       #I use this loop to make sure the user has enough money
                          #if they do not the program will ask for data again
    bill=Decimal(input("Enter the bill that needs to be paied"))
    payment=Decimal(input("Enter how much you paied in pounds and pence"))
    if payment<bill:            #This is for if the user has not got enough money
        print("Invalid funds")
    left=payment-bill



while left !=Decimal(0.00):
    print(left)
    if left>= 20:      #If there is more than a £20 difference
        left-=20
        out20P+=1
    elif left>= 10:      #If there is more than a £10 difference
        left-=10
        out10P+=1
    elif left>=5:      #If there is more than a £5 difference
        left-=5
        out5P+=1
    elif left>=1:      #If there is more than a £1 difference
        left-=1
        out1P+=1
        print(left)
    elif left>= 0.5:      #If there is more than a 50p difference
        left-=Decimal(0.50)
        out50p+=1
    elif left>=0.2:      #If there is more than a 20p difference
        left-=0.20
        out20p+=1
    elif left>=0.1:      #If there is more than a 10p difference
        left-=0.10
        out10p+=1
    elif left>=0.05:      #If there is more than a 5p difference
        left-=0.05
        out5p+=1
    elif left>= 0.02:      #If there is more than a 2p difference
        left-=0.02
        out2p+=1
    elif left>= 0.01:      #If there is more than a 1p difference
        left-=0.01
        out1p+=1

else:

    print ("You should have",out20P," of £20s")
    print ("You should have",out10P," of £10s")
    print ("You should have",out5P," of £5s")
    print ("You should have",out2P," of £2s")
    print ("You should have",out1P," of £1s")
    print ("You should have",out50p," of 50ps")
    print ("You should have",out20p," of 20ps")
    print ("You should have",out10p," of 10ps")
    print ("You should have",out5p," of 5ps")
    print ("You should have",out2p," of 2ps")
    print ("You should have",out1p," of 1ps")