Problem:
Score : 400 points

Problem Statement

There are N people standing in a queue from west to east.

Given is a string S of length N representing the directions of the people.
The i-th person from the west is facing west if the i-th character of S is L, and east if that character of S is R.

A person is happy if the person in front of him/her is facing the same direction.
If no person is standing in front of a person, however, he/she is not happy.

You can perform the following operation any number of times between 0 and K (inclusive):

Operation: Choose integers l and r such that 1 \leq l \leq r \leq N, and rotate by 180 degrees the part of the queue: the l-th, (l+1)-th, ..., r-th persons. That is, for each i = 0, 1, ..., r-l, the (l + i)-th person from the west will stand the (r - i)-th from the west after the operation, facing east if he/she is facing west now, and vice versa.

What is the maximum possible number of happy people you can have?

Constraints

N is an integer satisfying 1 \leq N \leq 10^5.

K is an integer satisfying 1 \leq K \leq 10^5.

|S| = N

Each character of S is L or R.

Input

Input is given from Standard Input in the following format:

N K
S

Output

Print the maximum possible number of happy people after at most K operations.

Sample Input 1

6 1
LRLRRL

Sample Output 1

3

If we choose (l, r) = (2, 5), we have LLLRLL, where the 2-nd, 3-rd, and 6-th persons from the west are happy.

Sample Input 2

13 3
LRRLRLRRLRLLR

Sample Output 2

9

Sample Input 3

10 1
LLLLLRRRRR

Sample Output 3

9

Sample Input 4

9 2
RRRLRLRLL

Sample Output 4

7

Solution in Rust (1.15.1) (judge verdict: Accepted)


fn solve(src: &str) -> String {
    let mut sc = Scanner::from_str(src);

    let n: usize = sc.read();
    let k: usize = sc.read();
    let mut s = sc.chars();

    let mut ctr = 0;
    let fix = s[0];
    let mut chg = false;
    for c in &mut s {
        if *c == fix {
            if chg {
                if ctr == k-1 {
                    break;
                } else {
                    chg = false;
                    ctr += 1;
                }
            }
        } else {
            chg = true;
            *c = fix;
        }
    }
    let mut ans = 0;
    for i in 0..n {
        match s[i] {
            'L' => {
                if i > 0 && s[i - 1] == 'L' {
                    ans += 1;
                }
            }
            'R' => {
                if i < n - 1 && s[i + 1] == 'R' {
                    ans += 1;
                }
            }
            _ => unreachable!(),
        }
    }

    format!("{}\n", ans)
}
#[test]
fn test_solve() {
    assert_eq!(solve("6 1\nLRLRRL\n"), "3\n");
    assert_eq!(solve("13 3\nLRRLRLRRLRLLR\n"), "9\n");
    assert_eq!(solve("10 1\nLLLLLRRRRR\n"), "9\n");
    assert_eq!(solve("9 2\nRRRLRLRLL\n"), "7\n");
}
fn main() {
    let mut buf = String::new();
    use std::io::Read;
    std::io::stdin().read_to_string(&mut buf).unwrap();
    use std::io::Write;
    std::io::stdout().write_all(solve(&buf).as_bytes()).unwrap();
}
struct Scanner<I> {
    src: I,
}
impl<'a> Scanner<std::str::SplitWhitespace<'a>> {
    fn from_str(src: &'a str) -> Self {
        Scanner {
            src: src.split_whitespace(),
        }
    }
}
#[allow(dead_code)]
impl<'a, I> Scanner<I>
where
    I: std::iter::Iterator<Item = &'a str>,
{
    fn read<T: std::str::FromStr>(&mut self) -> T {
        self.src.next().unwrap().parse().ok().expect("Parse error")
    }
    fn vec<T: std::str::FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.read()).collect()
    }
    fn chars(&mut self) -> Vec<char> {
        self.src.next().unwrap().chars().collect()
    }
}