There are six coupons numbered $$1$$ to $$6$$ and six envelopes, also numbered $$1$$ to $$6$$. The first two coupons are placed together in any one envelope. Similarly, the third and the fourth are placed together in a different envelope, and the last two are placed together in yet another different envelope. How many ways can this be done if no coupon is placed in the envelope having the same number as the coupon?