#include <iostream>

class progress
{
public:
	double a1;
	double d;
	virtual double summ(double n);
};

class aprogress : public progress
{
public:
	double summ(double n)
	{
		double an = a1 + (n - 1) * d;
		return (n + 1) * (a1 * an) / 2;
	}
};

class gprogress : public progress
{
public:
	double summ(double n)
	{
		double an = a1*d*n-1;
		return (a1-an*d)/(1-d);
	}
};

int main()
{
	return 0;
}