18432번 - JJOOII 2 서브태스크다국어

Bitaro received a string S of length N for his birthday present. String S consists of three kinds of characters, J, O and I.

For each positive integer K, we will call the string which consists of K J’s, K O’s, and K I’s in this order JOI-string of level K. For example, JJOOII is a JOI-string of level 2.

Bitaro likes a JOI-string of level K, so he is going to make a JOI-string of level K from string S by using the following three operations any number of times in arbitrary order:

• Operation 1 Bitaro deletes the first character of S.
• Operation 2 Bitaro deletes the last character of S.
• Operation 3 Bitaro deletes a character of S which is neither the first nor the last.

Because using Operation 3 is time-consuming, Bitaro wants to make a JOI-string of level K with as small number of Operation 3 as possible.

Write a program which, given a string S of length N and a positive integer K, prints the smallest number of Operation 3 required to make a JOI-string of level K from S . If it is impossible to make a JOI-string of level K with the operations, print −1 instead.

Read the following data from the standard input. N and K are integers. S is a string.

N K
S

Write one line to the standard output. The output should contain the smallest number of Operation 3 required to make a JOI-string of level K from S . If it is impossible to make a JOI-string of level K, print −1 instead.

• 3 ≤ N ≤ 200 000.
• 1 ≤ K ≤ N/3.
• S is a string of length N which consists of J, O and I.