KöMaL 2009 C981

The captain of a ship wrote down the formula $d=p\sqrt h$ in his log book for the distance to the horizon. Unfortunately, the number $p$ got blurred. $d$ denotes the distance to the horizon in kilometers, and $h$ stands for the height of the eyes of the observer above sea level in metres. Determine a value of $p$ that provides a practicable formula. (Use 6370 km for the radius of the Earth.)