시간 제한메모리 제한제출정답맞힌 사람정답 비율
1 초 128 MB101211520.270%

문제

동혁이는 자석을 매우 좋아하고, 자석을 이용해서 매우 독특한 실험을 한다. 동혁이가 가지고 있는 자석은 작은 막대처럼 생겼다. 자석은 길이가 1이고, 두 자극(S극과 N극)을 가지고 있다. 자석은 같은 극끼리는 붙지 않지만, 다른 극끼리는 서로 붙는다. 이 자석은 매우 강력한 자석이기 때문에, 한 번 붙으면 다시 뗄 수 없다.

실험을 시작하기 전에 동혁이는 N개의 자석을 바닥에 놓는다. 그 다음 실험을 시작하면 다른 극을 마주 보고 있는 자석은 모두 붙는다. 자석은 실험을 시작하기 전에는 붙지 않는다. 또, 실험을 시작한 후, 붙은 자석은 뗄 수 없다.

예를 들어, 동혁이가 실험을 시작하기 전에 자석 6개를 다음과 같이 놓았다고 생각해보자.

동혁이가 실험을 시작하면, 자석은 다음과 같이 붙게된다.

사실 동혁이는 길이가 정확히 L인 자석이 필요해서 이 실험을 시작하게 된 것이다. 동혁이가 자석을 놓은 초기 배치가 주어졌을 때, 몇 개의 자석을 뒤집으면 길이가 정확히 L인 자석을 얻을 수 있는지 구하는 프로그램을 작성하시오. 만약, 여러 가지 경우가 있다면 뒤집는 횟수가 가장 작은 것을 출력한다.

입력

첫째 줄에 자석의 수 N과 동혁이가 만들려고 하는 자석의 길이 L이 주어진다. (1 ≤ N ≤ 500000, 1 ≤ L ≤ N)

다음 줄에는 초기 자석의 배치를 나타내는 문자열 "NS" 또는 "SN"이 N개가 주어진다.

항상 답이 존재하는 경우만 주어진다.

출력

길이가 정확히 L인 자석을 만들기 위해서 필요한 뒤집는 횟수의 최솟값을 출력한다.

예제 입력 1

6 4
NS SN NS SN SN NS

예제 출력 1

1

예제 입력 2

4 4
NS SN NS SN

예제 출력 2

2

예제 입력 3

15 13
SN NS NS SN NS SN SN NS NS SN SN NS NS NS SN

예제 출력 3

3
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(1 &le; N &le; 500000, 1 &le; L &le; N)<\/p>\r\n\r\n<p>\ub2e4\uc74c \uc904\uc5d0\ub294 \ucd08\uae30 \uc790\uc11d\uc758 \ubc30\uce58\ub97c \ub098\ud0c0\ub0b4\ub294 \ubb38\uc790\uc5f4 &quot;NS&quot; \ub610\ub294 &quot;SN&quot;\uc774 N\uac1c\uac00 \uc8fc\uc5b4\uc9c4\ub2e4.<\/p>\r\n\r\n<p>\ud56d\uc0c1 \ub2f5\uc774 \uc874\uc7ac\ud558\ub294 \uacbd\uc6b0\ub9cc \uc8fc\uc5b4\uc9c4\ub2e4.<\/p>\r\n","output":"<p>\uae38\uc774\uac00 \uc815\ud655\ud788 L\uc778 \uc790\uc11d\uc744 \ub9cc\ub4e4\uae30 \uc704\ud574\uc11c \ud544\uc694\ud55c \ub4a4\uc9d1\ub294 \ud69f\uc218\uc758 \ucd5c\uc19f\uac12\uc744 \ucd9c\ub825\ud55c\ub2e4.<\/p>\r\n","hint":"","original":"0","html_title":"0","problem_lang_tcode":"Korean"},{"problem_id":"3144","problem_lang":"1","title":"MAGNETI","description":"<p>The crazy scientist Matija is performing crazy experiments with even crazier magnets. Each magnet looks like a small stick. It is 1 unit long and has two magnetic poles, South (S) and North (N). 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