In a computer game, each gamer has an army of units.
Write a program that will classify the army of your enemies corresponding to the following rules:
Units: Category
less than 1: no army
from 1 to 19: pack
from 20 to 249: throng
from 250 to 999: zounds
1000 and more: legion
The program should read the number of units and output the corresponding category.