What are elongated hyphens? Which sentence demonstrates the correct use of elongated hyphens?

Elongated hyphens would make this sentence grammatically correct: Gideon and Francis took a difficult but not interesting science course.

Gideon – and – Francis took a difficult but not interesting science course.

Gideon and Francis took a difficult but not – interesting science – course.

Gideon and Francis took a difficult – but not interesting – science course.

Gideon and Francis - took a difficult – but not interesting science course.?