double sqrt_a(double a, double eps)
{
    if (a == 0)
        return 0;

    double x_1 = a;
    double x_next = (x_1 + a / x_1) / 2;
    double x_current = x_1;

    while (abs(x_next - x_current) >= eps)
    {
        x_current = x_next;
        x_next = (x_current + a / x_current) / 2;
    }

    return x_next;
}

int main()
{
    std::cout << std::setprecision(9)  << sqrt_a(120.1, 0.000000001) << std::endl;
    std::cout << sqrt(120.1);
}