s = input()
x = {
    "A": 10,
    "B": 11,
    "C": 12,
    "D": 13,
    "E": 14,
    "F": 15
}
num = 0
for ind, i in enumerate(s[-1:1:-1]):
    num += int(x.get(i, i))*16**(ind)
print(num)

不用内置16进制，有相对简洁