Locus of a point

Let $A$ be a point. Square 1 is a square centered at $A$ . Square 2 is a square such that one vertex of square 2 is $A$ , and the center of square 2 lies on the border of square 1. What shape does the set of all points that can be the vertex directly opposite $A$ in square 2 form?

1. A square
2. The border of a square
3. A circle
4. The border of a circle