1double mysqrt(const double input, double approximation = 1, unsigned int iterations = 8)
 2{
 3	if (input < 0 || approximation <= 0)
 4	{
 5		throw std::runtime_error("Input and approximation should bigger than zero.");
 6	}
 7
 8	double y;
 9	double k;
10	for (unsigned int i = 0; i < iterations; ++i)
11	{	
12		y = approximation * approximation - input;
13		k = 2 * approximation;
14		approximation = -y / k + approximation;	
15		//approximation = -(approximation * approximation - input) / (2 * approximation) + approximation;
16	}
17        return approximation;
18}