Problem 45991. Find the position of planet in solarsystem

Write a funtion named nthplanet which takes name of the planet as input string and provides the position of the planet, starting from Mercury at 1st position and Neptune at 8th , as output.(For those who are sad because I ignored Pluto, Pluto is considered as Dwarf planet by IAU)

If

x = 'Earth'

then

nthplanet(x)

gives

3

Please have a look at the Testsuite before you begin