How perform overloading and overriding in WCF? What is different between both in WCF? [Resolved]

//Error - will throw an InvalidOperationException while hosting
[ServiceContract]
public interface MyService
{
    [OperationContract]
    int Sum(int x, int y);

    [OperationContract]
    int Sum(double x, double y);
}

//Valid one
[ServiceContract]
public interface MyService
{
    [OperationContract(Name="SumUsingInt")]
    int Sum(int x, int y);

    [OperationContract(Name="SumUsingDouble")]
    int Sum(double x, double y);
}