Given the following context:

Other early Welsh Arthurian texts include a poem found in the Black Book of Carmarthen, "Pa gur yv y porthaur?" ("What man is the gatekeeper?"). This takes the form of a dialogue between Arthur and the gatekeeper of a fortress he wishes to enter, in which Arthur recounts the names and deeds of himself and his men, notably Cei (Kay) and Bedwyr (Bedivere). The Welsh prose tale Culhwch and Olwen (c. 1100), included in the modern Mabinogion collection, has a much longer list of more than 200 of Arthur's men, though Cei and Bedwyr again take a central place. The story as a whole tells of Arthur helping his kinsman Culhwch win the hand of Olwen, daughter of Ysbaddaden Chief-Giant, by completing a series of apparently impossible tasks, including the hunt for the great semi-divine boar Twrch Trwyth. The 9th-century Historia Brittonum also refers to this tale, with the boar there named Troy(n)t. Finally, Arthur is mentioned numerous times in the Welsh Triads, a collection of short summaries of Welsh tradition and legend which are classified into groups of three linked characters or episodes to assist recall. The later manuscripts of the Triads are partly derivative from Geoffrey of Monmouth and later continental traditions, but the earliest ones show no such influence and are usually agreed to refer to pre-existing Welsh traditions. Even in these, however, Arthur's court has started to embody legendary Britain as a whole, with "Arthur's Court" sometimes substituted for "The Island of Britain" in the formula "Three XXX of the Island of Britain". While it is not clear from the Historia Brittonum and the Annales Cambriae that Arthur was even considered a king, by the time Culhwch and Olwen and the Triads were written he had become Penteyrnedd yr Ynys hon, "Chief of the Lords of this Island", the overlord of Wales, Cornwall and the North.In addition to these pre-Galfridian Welsh poems and tales, Arthur appears in some other early Latin texts besides the Historia Brittonum and the Annales Cambriae. In particular, Arthur...

answer the following question:

What is the exact title of the story that tells of Arthur helping his kinsman Culhwch win the hand of Olwen, daughter of Ysbaddaden Chief-Giant, by completing a series of apparently impossible tasks? 

Culhwch and Olwen