def checksum():
    original = input("\nPlease enter a checksum (only hex digits are accepted):\n")
    encoded = ""
    divide=[]
    converted=[]
    total_decimal=[]
    error=""
    for i in range(len(original)):
        if original[i] in "0123456789abcdef":
            encoded += original[i]
        else:
            error += "Invalid character detected"
            return error

    while encoded:
        divide.append(encoded[:4])
        encoded = encoded[4:]

    if len(divide[-1])!=4:
        error += "There is an irregular number of digits"
        return error

    for i in range(len(divide)):
        converted.append([])
        for j in range(0, 4):
             if(divide[i][j]=="a"):
                converted[i].append(10)
             elif(divide[i][j]=="b"):
                 converted[i].append(11)
             elif(divide[i][j] == "c"):
                 converted[i].append(12)
             elif(divide[i][j] == "d"):
                 converted[i].append(13)
             elif(divide[i][j] == "e"):
                 converted[i].append(14)
             elif(divide[i][j] == "f"):
                 converted[i].append(15)
             else:
                converted[i].append(int(divide[i][j]))

    for i in range(len(converted)):
        for j in range(0, 3):
            total_decimal[i]+=converted[i][j]


    return total_decimal

print(checksum())