letters = ["a", "b", "c", "d"]

print(letters[0])
print(letters[-1])
letters[0] = 'A'
print(letters)
print(letters[0:3])
print(letters[:3])
print(letters[::2])


# example
number = list(range(20))
print(number)
print(number[0:20:2])
print(number[::-1])
