def cut_sentence(line, length):
    """
    Cut a given sentence, so it becomes shorter than or equal to a given length.
    """
    if length >= len(line):
        return line
    if line[length] == " ":
        return line[:length]+"..."
    line = line[:length].split(" ")
    line.pop()
    return " ".join(line)+"..."


if __name__ == '__main__':
    # These "asserts" using only for self-checking and not necessary for auto-testing
    assert cut_sentence("Hi my name is Alex", 4) == "Hi...", "First"
    assert cut_sentence("Hi my name is Alex", 8) == "Hi my...", "Second"
    assert cut_sentence("Hi my name is Alex", 18) == "Hi my name is Alex", "Third"
    assert cut_sentence("Hi my name is Alex", 20) == "Hi my name is Alex", "Fourth"
    print('Done! Do you like it? Go Check it!')