struct S
    {
        int x;
        int freq;

        S(int X, int F)
        {
            x = X, freq = F;
        }
    };
    bool compare(const S &a, const S &b)
    {
        if (a.freq != b.freq) return a.freq > b.freq;
        return a.x < b.x;
    }
    int main()
    {
        std::set<S> my_set;       //custom compare

        my_set.find(S(10, 11));   //find first element with x = 10
        my_set.insert(S(20, 30)); //normal insertion
        my_set.erase(S(20, 30));  //erase element with x = 20 && freq = 30

        cout << my_set.size() << endl;

    }