void Start(){
    dragDistance = Screen.height*20/100; //dragDistance is 20% height of the screen
}

void Update(){

    foreach (Touch touch in Input.touches)  //use loop to detect more than one swipe
    { //can be ommitted if you are using lists
        if (touch.phase == TouchPhase.Began) //check for the first touch
{
    fp = touch.position;
    lp = touch.position;

}

        if (touch.phase == TouchPhase.Moved) //add the touches to list as the swipe is being made
        {
            touchPositions.Add(touch.position);
        }

        if (touch.phase == TouchPhase.Ended) //check if the finger is removed from the screen
        {
            //lp = touch.position;  //last touch position. Ommitted if you use list
            fp =  touchPositions[0]; //get first touch position from the list of touches
            lp =  touchPositions[touchPositions.Count-1]; //last touch position

            //Check if drag distance is greater than 20% of the screen height
            if (Mathf.Abs(lp.x - fp.x) > dragDistance || Mathf.Abs(lp.y - fp.y) > dragDistance)
            {//It's a drag
                //check if the drag is vertical or horizontal
                if (Mathf.Abs(lp.x - fp.x) > Mathf.Abs(lp.y - fp.y))
                {   //If the horizontal movement is greater than the vertical movement...
                    if ((lp.x>fp.x))  //If the movement was to the right)
                    {   //Right swipe
                        Debug.Log("Right Swipe");
                    }
                    else
                    {   //Left swipe
                        Debug.Log("Left Swipe");
                    }
                }
                else
                {   //the vertical movement is greater than the horizontal movement
                    if (lp.y>fp.y)  //If the movement was up
                    {   //Up swipe
                        Debug.Log("Up Swipe");
                    }
                    else
                    {   //Down swipe
                        Debug.Log("Down Swipe");
                    }
                }
            }
        }
        else
        {   //It's a tap as the drag distance is less than 20% of the screen height

        }
    }
}