class Solution:
    def addBinary(self, a: str, b: str) -> str:
        a = a[::-1]
        b = b[::-1]
        carry = 0
        c = ""
        for i in range(max(len(a), len(b))):
            d = carry + int(a[i]) + int(b[i])
            if d == 3:
                c = c + "1"
                carry = 1
            if d == 2:
                c = c + "0"
                carry = 1
            if d == 1:
                c = c + "1"
                carry = 0
            if d == 0:
                c = c + "0"
                carry = 0
            else:
                print(d)
                raise Exception

        return(c[::-1])