def sort(l: list):
    l = list(l)
    l.sort()
    return l


def sort_even(l: list):
    """This function takes a list l and returns a list l' such that
    l' is identical to l in the odd indicies, while its values at the even indicies are equal
    to the values of the even indicies of l, but sorted.
    >>> sort_even([1, 2, 3])
    [1, 2, 3]
    >>> sort_even([5, 6, 3, 4])
    [3, 6, 5, 4]
    
    Example solution:
    # line 1
    evens = l[::2]
    # line 2
    odds = l[1::2]
    # line 3
    evens.sort()
    # line 4
    ans = []
    # line 5
    for e, o in zip(evens, odds):
        # line 6
        ans.extend([o, e])
    # line 7
    if len(evens) > len(odds):
        # line 8
        ans.append(evens[-1])
    # line 9
    return ans
    
    """
    # Please print out which line of the above program contains an error. E.g. if the bug is on line 4 then print 4
    # END OF CONTEXT
    print("6")
    # END OF SOLUTION

def check(candidate):

    import io
    from contextlib import redirect_stdout

    f = io.StringIO()
    with redirect_stdout(f):
        candidate([])
    out = f.getvalue().strip('\n')

    assert "6" == out
    for i in range(0, 10):
        if i != 6:
            assert str(i) != out

if __name__ == '__main__':
    check(sort_even)
