訓 ただ(し) ・ 音 タン
Sino-Vietnamese: đãn
The person radical 亻 with 旦 giving the sound: 但し means "however", adding a condition to what was said.
Stroke data: KanjiVG (CC BY-SA 3.0) — kanjivg.tagaini.net
参加は自由です。但し、予約が必要です。 (さんかはじゆうですただしよやくがひつようです)
Participation is free. However, a reservation is required.