import string


def get_num_let(let):
    """
    Returns the integer corresponding to the input letter
    """
    alphabet = string.ascii_lowercase

    if len(let) == 1:
        return alphabet.index(let)
    if len(let) == 2:
        return 26 * (alphabet.index(let[0])) + alphabet.index(let[1]) + 26
    if len(let) == 3:
        return (26 * 26 * (alphabet.index(let[0])) + 26 *
                (alphabet.index(let[1])) + alphabet.index(let[2]) + 26 * 26 +
                26)
    else:
        raise RuntimeError('letter does not contain' + ' 1,2 or 3 letters')