There are 7 bags of rice, their weights are 12kg, 15kg, 17kg, 20kg, 22kg, 24kg, 26kg respectively. A buys one bag first, and B, C, and D buy the rest. It is known that the weights bought by B and C are exactly equal, which are twice that of D. Find the weight of the bag of rice that A bought first.
有7袋大米，它们的重量分别是12kg、15kg、17kg、20kg、22kg、24kg、26kg．甲先买走一袋，剩下的由乙、丙、丁三人买走．已知乙和丙买走的重量恰好相等，都是丁的2倍．求甲先买走的那一袋大米的重量．
<result>26</result>