#### 二进制/十进制转换 ####

#### 从十进制到二进制 #####

##num = int(input("An positive integer: "))
##n = num
##bits = ""
##while n != 0:
##    if n % 2 == 0:
##        bits = "0" + bits
##    else:
##        bits = "1" + bits
##    n //= 2
##
##print("Binary code of", num, "is", bits)


#### 从二进制到十进制 #####

bits = input("A binary string: ")

num = 0
for i in range(len(bits)):
    num = num * 2 + int(bits[i])

print("Number of", bits, "is", num)


###### 从二进制到十进制 #####
##
##bits = input("A binary string: ")
##
##num = 0
##for c in bits: # str 可以用作迭代器
##    num = num * 2 + int(c)
##
##print("Number of", bits, "is", num)