贝西收集了N颗石头，每颗石头上都有一个字母，贝西想把这些石头做成项链。
贝西的身边有另一只奶牛，这只奶牛的名字是一个长度为M的字符串，贝西不希望这只牛的名字出现在她的项链上(项链的子串)，她想知道，最少删掉几颗石头就可以避免这种情况发生。
* Line 1: The first line is a length-N string describing Bessie's initial necklace; each character is in the range "a" through "z".
* Line 2: The second line is the length-M name of the other cow in the barn, also made of characters from "a" to "z".
ababaa
aba 1 For at least 20% of test cases, N <= 20. For at least 60% of test cases, N <= 1000, M <= 100. For all test cases, N <= 10000, M <= 1000. For all test cases, M <= N.
The modified necklace should be "abbaa".