Python3 Solution
Code\n\nclass Solution:\n    def greatestLetter(self, s: str) -> str:\n        s_set = set()\n        for i in s :\n            if i.isupper() :\n              
# Code\n```\nclass Solution:\n    def greatestLetter(self, s: str) -> str:\n        s_set = set()\n        for i in s :\n            if i.isupper() :\n                if i.lower() in s :\n                    s_set.add(i)\n        if s_set :\n            return max(s_set)\n        return ""\n        \n```
['Python3']