Finding Nearest Object Both Positive And Negative?

Hi,

I'm trying to find the closest point to where the mouse is clicked (topArrow, bottomArrow etc are Vector3 points on screen).

The problem is no matter where I click, it either says rightArrow or topArrow are closest; this is because they are both in the positive direction.

How can I fix this to return the actual closest?

 Vector3 topArrow = new Vector3(0,12,0);
 Vector3 bottomArrow = new Vector3(0,-12,0);
 Vector3 leftArrow = new Vector3(-30,0,0);
 Vector3 rightArrow = new Vector3(30,0,0);

 Vector3 getNearestArrow()
     {
         Vector3 closestPos = new Vector3(0,0,0);
         float closestDistance = Mathf.Infinity;
         
         if(Vector3.Distance (topArrow,Input.mousePosition) < closestDistance)
         {
             closestDistance = Vector3.Distance (topArrow,Input.mousePosition);
             closestPos = topArrow;
         }
         
         if(Vector3.Distance (bottomArrow,Input.mousePosition) < closestDistance)
         {
             closestDistance = Vector3.Distance (bottomArrow,Input.mousePosition);
             closestPos = bottomArrow;
         }
         
         if(Vector3.Distance (leftArrow,Input.mousePosition) < closestDistance)
         {
             closestDistance = Vector3.Distance (leftArrow,Input.mousePosition);
             closestPos = leftArrow;
         }
         
         if(Vector3.Distance (rightArrow,Input.mousePosition) < closestDistance)
         {
             closestDistance = Vector3.Distance (rightArrow,Input.mousePosition);
             closestPos = rightArrow;
         }
                             
         return closestPos;
     }