Which of the following is the correct implementation of the interface given below?

interface IMyInterface
{ 
    double MyFun(Single i);
}

class MyClass
{
    double MyFun(Single i) as IMyInterface.MyFun
    {
        // Some code
    }
}

class MyClass 
{
    MyFun (Single i) As Double
    {
        // Some code
    } 
}

class MyClass: implements IMyInterface
{
    double fun(Single si) implements IMyInterface.MyFun()
    {
        //Some code
    } 
}

class MyClass: IMyInterface
{
    double IMyInterface.MyFun(Single i)
    {
        // Some code
    } 
}