class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        unordered_set<int> S;
        for(auto x:nums)S.insert(x);
        int res=0;
        for(auto x:nums)
        {
            if(S.count(x)&&!S.count(x-1))
            {
                int y=x;
                S.erase(x);
                while(S.count(y+1)){y++;S.erase(y);}
                res = max(res, y-x+1);
            }
        }
        return res;
    }
};