Xiaogang practiced addition and abacus, using 1+2+3+..., when a certain number is reached, the sum is 1000. When checking the calculation, it is found that a number has been added repeatedly. What is the number?
小刚进行加法珠算练习，用1+2+3+…，当数到某个数时，和是1000．在验算时发现重复加了一个数，这个数是多少．
<result>10</result>