class Solution:
    def largestGoodInteger(self, num: str) -> str:
        if not num or len(num) <= 2:
            return ""

        ans = -1
        for i, c in enumerate(num):
            if i <= len(num)-3 and num[i] <mark> num[i+1] and num[i] </mark> num[i+2]: # 012, 3 - 3 = 0
                ans = max(int(num[i:i+3]), ans)

        if ans == -1:
            return ""
        if ans == 0:
            return "000"
        return str(ans)