class Solution(object):
    def exec(self, equation):
        vars = None
        eqList = list(equation)
        denth = 0
        for i,each in enumerate(equation):
            if each in "abcdefghijklmnopqrstuvwxyz":
                vars = each
                if i == 0:
                    continue
                if equation[i-1] in ‘1234567890‘:
                    eqList.insert(i + denth, ‘*‘)
                    denth += 1

        equation = ‘‘.join(eqList)
        equation1 = equation.replace("=", "-(") + ")"
        c = eval(equation1, {vars: 1j})
        return -c.real/c.imag  

s = Solution()

print(s.exec("3a-1 =a+2"))