face gameobject to mouse (touch) drag direction

i have a game object in my scene
i want to rotate it to up if i moving my finger (or mouse) to up
if i drag to left i want my game object face left

<< i have a image to explain better >>

sorry for my bad english

(i want to create a controll like flaming core game)

Vector3 startPos;
Vector3 endPos;

void OnMouseDown()
   startPos = Input.mousePosition;

void OnMouseUp()
   endPos= Input.mousePosition;
   transform.forward = endPos - startPos;