Bagaimana untuk mengisytiharkan fungsi ahli dalam antara muka C#?

public interface InterfaceName {
   // interface members
   void InterfaceMemberOne();
   double InterfaceMembeTwo();
   void InterfaceMemberThree()
}

public class ClassName: InterfaceName {
   void InterfaceMemberOne() {
      // interface member
   }
}

void InterfaceMemberOne();
double InterfaceMembeTwo();
void InterfaceMemberThree()

public class ClassName: InterfaceName {
   void InterfaceMemberOne() {
      // interface member
   }
}