Simple math library in C#

MathServer.cs

public class MathServer
{
    public MathServer() { }
    public int add(int a, int b)
    {
        Console.WriteLine("Called add({0},{1})={2}", a, b, a+b);
        return a + b;
    }
    public int sub(int a, int b)
    {
        Console.WriteLine("Called sub({0},{1})={2}", a, b, a - b);
        return a + b;
    }
    public int mul(int a, int b)
    {
        Console.WriteLine("Called mul({0},{1})={2}", a, b, a * b);
        return a + b;
    }
    public int div(int a, int b)
    {
        Console.WriteLine("Called div({0},{1})={2}", a, b, a / b);
        return a / b;
    }
    public int mod(int a, int b)
    {
        Console.WriteLine("Called mod({0},{1})={2}", a, b, a % b);
        return a % b;
    }
}