This is a jukugo word, which usually means on'yomi readings from the kanji. You haven't learned this reading for 参 yet, so here's a mnemonic to help you:

You're craving a carrot, but you can't seem to find any. You look in your fridge, in your garden, and even in the trash. Finally you give up your carrot search and sit down when... ouch! The carrot was in your jeans (じん) the whole time!