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문제

A word s composed of (2n + n - 1) characters 0 and 1 is called a de Bruijn sequence of order n if every n-character word composed of zeroes and ones is its subword - that is a fragment of consecutive characters - of s. An example of a de Bruijn sequence of order 3 is 0001011100.

A type two de Bruijn sequence of order n is such a word s of arbitrary length that each n-character word composed of zeroes and ones is a subsequence - that is a fragment of not necessarily consecutive characters - of s. An example of a type two de Bruijn sequence of order 3 is 00101101. As far as we know, Nicolaas Govert de Bruijn did not invent such sequences, but their definition is similar to the previous one, isn't it?

Let us consider a word s composed only of zeroes and ones. How many digits (0 or 1, of course) have to be added at the end of s for the word to become a type two de Bruijn sequence of order n?

입력

The first line of the standard input contains two integers m and n (1 ≤ m, n ≤ 1,000,000), separated by a single space. The second line contains an m-character word s composed only of digits 0 and 1 that does not contain any spaces.

출력

The first and only line of the standard output should contain a single non-negative integer, denoting the minimal number of digits that need to be added at the end of the word s for it to become a t.t.d.B.s. of order n.

예제 입력 1

5 3
00101

예제 출력 1

2

힌트

After adding the characters 01 we obtain the following t.t.d.B.s. of order 3: 0010101.