There are 8 boxes, and each box contains the same kind of pens. The numbers of pens in the 8 boxes are 17, 23, 33, 36, 38, 42, 49, and 51. Among these pens, the number of ballpoint pens is twice the number of pens, the number of pens is 1/3 of that of pencils, and there is only one watercolor pen in the box. How many watercolor pens are there in this box?
有8只盒子，每只盒内放有同一种笔.8只盒子所装笔的支数分别为17支、23支、33支、36支、38支、42支、49支、51支．在这些笔中，圆珠笔的支数是钢笔的支数的2倍，钢笔支数是铅笔支数的(1/3)，只有一只盒里放的水彩笔．这盒水彩笔共有多少支．
<result>49</result>