# function to convert from hexidecimal string to integer:

def hexdec(H):
    i = len(H)-1;    # loop counter, start at last character
    dec = 0;         # decimal number to be computed
    digit=0          # variable to hold dec value for each digit
    power = 0        # the power of 16 currently being computed
    while i>=0:
        # first convert character to a numerical value
        ac = ord(H[i])   # ac is ascii code of character
        if (ac>=48 and ac<=57): # digits 0-9:
            digit = ac-48
        else:
            if (ac>=65 and ac<=70): # digits A-F
                digit = 10 + (ac-65)
            else:
                raise Exception("invalid input: ",H)  # abort program
        # at this point digit is from 0 to 15
        dec = dec + digit*(16**power)
        power = power+1
        i = i-1
    #end while
    return dec
#end hexdec


print hexdec("4F")
print hexdec("E0D8")
print hexdec("00FF")

# function to convert from integer to hexidecimal string
def dechex(D):
    digits = "0123456789ABCDEF"    # string to hold all hex digits
    Hex = ""                       # return value: constructed char by char
    if (D==0): return "0"          # special case
    while (D!=0):
        dv = D % 16      # value of one digit  0-15
        hv = digits[dv]  # corresponding hex digit: 0-F
        Hex = hv+Hex     # add char to left end of string
        D = D/16         # go to next digit
    #end while
    return Hex
# end dechex

print "\n", dechex(72)
print dechex(255)
print dechex(65535)
print dechex(400)