# Write a procedure, shift_n_letters which takes as its input a lowercase
# letter, a-z, and an integer n, and returns the letter n steps in the
# alphabet after it. Note that 'a' follows 'z', and that n can be positive,
#negative or zero.

def shift_n_letters(letter, n):
    alphabet = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z']
    return alphabet[(alphabet.index(letter) + n) % 26]

print (shift_n_letters('s', 1))
#>>> t
print (shift_n_letters('s', 2))
#>>> u
print (shift_n_letters('s', 10))
#>>> c
print (shift_n_letters('s', -10))
#>>> i
