Sphere, float Learn programming C#

using System;
public class exercise59
{
    public static void Main()
    {
        float radius;
        float pi = 3.1415926535f;

        Console.Write("Radius? ");
        radius = Convert.ToSingle(Console.ReadLine());

        Console.WriteLine(4 * pi * (radius * radius));

        Console.WriteLine(4 / 3 * pi * (radius * radius * radius));
    }
}