#include <cassert>

struct Base {
    int convert(int) const { return 1; }
    virtual int value(int n = 1) const { return n; }
    virtual ~Base() = default;
};

struct Derived : Base {
    using Base::convert;
    int convert(double) const { return 2; }
    int value(int n = 2) const override { return n * 10; }
};

int main() {
    Derived d;
    const Base& b = d;
    assert(d.convert(3) == 1);
    assert(d.convert(3.5) == 2);
    assert(b.value() == 10);
    assert(d.value() == 20);
    assert(d.Base::value() == 1);
}