Of course, I'll willingly help you, even though I'm going to stay there only for a couple of weeks.

willingly 是形容词 willing（乐意的、自愿的）加上副词后缀 -ly 构成的副词形式，表示"乐意地、心甘情愿地"。这个词强调帮助的行为是出于自愿而非被迫。