Move to C++20 and force std::cin with

    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

template <class T> class AddElements {
    T data;
public:
    AddElements(T value) : data(value) {}

    T add(T a) {
        data += a;
        return data;
    }
};

template <> class AddElements<string> {
public:
    string s;

    AddElements(const string& value): s(value) {}
    AddElements(string&& value): s(std::move(value)) {}

    string concatenate(const string& a) {
        return s.append(a);
    }
};