Problem with overloading operator+

Question

Hello.
I wrote the code below:

 public static Point operator +(Point p1, Point p2)
        {
            return new Point(p1.X + p2.X, p1.Y + p2.Y);
        }

But Creates error below on "operator+" :
One of the parameters of a binary operator must be the containing type

What's the problem?

Thanks.