51 students voted for a monitor, and the result of counting 40 of them was: A got 18 votes, B got 12 votes, and C got 10 votes. How many more votes does A have at least to ensure that he is elected as the squad leader with the most votes.
51个同学投票选一名班长，统计其中40张选票的结果是：甲得18票，乙得12票，丙得10票．甲至少再得多少张票，才能保证以得票数最多当选班长．
<result>3</result>