Convert from royal foot to league [nautical]

Unit Definition (royal foot)
The royal foot is a French pied de roi, also called the Paris foot in English.

Unit Definition (league [nautical])
The nautical league is approximately equal to three nautical miles, 1/20 degree, or 5556 meters (metres). Note that it is not equivalent to the portugese, french and spanish measurements of the league. The nautical league is also different from the league defined on land.