class Solution:
    def maximum69Number (self, num):
        new_num = ""
        done = False
        for c in str(num):
            if c == "6" and not done:
                new_num += "9"
                done = True
            else:
                new_num += c
          
        return int(new_num)

s = Solution()
print("Expected: 9999")
print("Got:", str(s.maximum69Number(9699)))