#include <iostream>
#include <set>

struct A {
    int i = 0;
    bool operator()(int a, int b)
    {
        ++i;
        return a < b;
    }
};

int main()
{    
    A a;

    std::set<int, A> s(a);

	for (int j = 0; j < 10; ++j) {
		int const prev = s.key_comp().i;
		s.insert(j);
		std::cout << j << ": " << (s.key_comp().i - prev) << "\n";
	}
}