Console Input Output Task 6

using System;
class CuadraticEquision
{
    static void Main()
    {
        int a = int.Parse(Console.ReadLine());
        int b = int.Parse(Console.ReadLine());
        int c = int.Parse(Console.ReadLine());
        double d = b*b - (4 * a * c);
        double x1, x2;
        if ((d > 0 ) && (a != 0))
        {
            x1 = ((-b) + Math.Sqrt(d)) / 2*a;
            x2 =((-b) - Math.Sqrt(d)) / 2 *a;
            Console.WriteLine("the equision has two roots: {0} and {1}.", x1, x2);
        }

        else if((a == 0) || (d < 0))
        {
            Console.WriteLine("This is not a quadratic equision or the equision has no real roots!");
        }

        else if (d == 0)
        {
            Console.WriteLine("This equision has one root: x = {0}.",(-b)/(2*a));
        }
    }
}