Write the three-digit \overline{3ab} repeatedly, write 1993 \overline{3ab} in total, the resulting number is exactly divisible by 91, find \overline{ab}.
将三位数\overline{3ab}重复写下去，一共写1993个\overline{3ab}，所得的数正好能被91整除，求\overline{ab}．
<result>64</result>