using namespace std;

class ClassConst : public Expression {
private:
    int num;
    ExpressionPtr prev = nullptr;
    ExpressionPtr next = nullptr;

public:
    ClassConst(int input) {
        num = input;
    }
    int Evaluate() const override {
        return num;
    }
    string ToString() const override {
        return to_string(num);
    }
};

class ClassSum : public Expression {
public:
    ExpressionPtr prev;
    ExpressionPtr next;
    ClassSum(ExpressionPtr first, ExpressionPtr second) {
        prev = first;
        next = second;
    }
    int Evaluate() const override {
        return prev->Evaluate() + next->Evaluate();
    }
    string ToString() const override {
        string result;
        result = prev->ToString() + " + " + next->ToString();
        return result;
    }
};

class ClassProduct : public Expression {
public:
    ExpressionPtr prev;
    ExpressionPtr next;
    ClassProduct(ExpressionPtr first, ExpressionPtr second) {
        prev = first;
        next = second;
    }
    int Evaluate() const override {
        return prev->Evaluate() * next->Evaluate();
    }
    string ToString() const override {
        string result;
        auto tmp = prev.get();
        if (typeid(*tmp) == typeid(ClassSum)) {
            result = '(' + prev->ToString() + ')';
        } else {
            result = prev->ToString();
        }
        result += " * ";
        tmp = next.get();
        if (typeid(*tmp) == typeid(ClassSum)) {
            result += '(' + next->ToString() + ')';
        }
        else {
            result += next->ToString();
        }
        return result;
    }
};

ExpressionPtr Const(int num) {
    ExpressionPtr a(new ClassConst(num));
    return a;
}

ExpressionPtr Sum(ExpressionPtr first, ExpressionPtr second) {
    ExpressionPtr a(new ClassSum(first, second));
    return a;
}
ExpressionPtr Product(ExpressionPtr first, ExpressionPtr second) {
    ExpressionPtr a(new ClassProduct(first, second));
    return a;
}