#[allow(unused_imports)]
use std::char::from_digit;
#[allow(unused_imports)]
use std::cmp::{max, min};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::fs::File;
#[allow(unused_imports)]
use std::io::prelude::*;
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufReader, BufWriter, Stdin, Stdout, Write};
#[allow(unused_imports)]
use std::mem::swap;
#[allow(unused_imports)]
use std::str::FromStr;

type BoxResult<T> = Result<T, Box<std::error::Error>>;

fn main() {
    let mut scanner = Scanner::new(stdin());
    let param = scanner.read_vector::<usize>().unwrap();
    let (n, k) = (param[0], param[1]);
    let s = scanner.read_chars().unwrap();
    let default = (0..n).fold(0, |acc, i| if is_happy(i, &s) { acc + 1 } else { acc });
    if s[0] == s[n - 1] {
        if let Some(count) = calc(&s, k, s[0] != 'L') {
            println!("{}", min(default + count, n - 1));
        } else {
            println!("{}", n - 1);
        }
    } else {
        let l = if let Some(count) = calc(&s, k, true) {
            min(default + count, n - 1)
        } else {
            n - 1
        };
        let r = if let Some(count) = calc(&s, k, false) {
            min(default + count, n - 1)
        } else {
            n - 1
        };
        println!("{}", max(l, r));
    }
}

fn is_happy(i: usize, s: &[char]) -> bool {
    if s[i] == 'L' && i > 0 && s[i - 1] == 'L' {
        true
    } else if s[i] == 'R' && i < s.len() - 1 && s[i + 1] == 'R' {
        true
    } else {
        false
    }
}

fn calc(s: &[char], mut k: usize, start_with_l: bool) -> Option<usize> {
    let mut nxt = if start_with_l { 'L' } else { 'R' };
    let (mut l, mut r) = (0, s.len() - 1);
    let mut count = 0;
    while k > 0 && l < r {
        while l < r {
            if s[l] == nxt {
                break;
            }
            l += 1;
        }
        if l == r {
            break;
        }
        while l < r {
            if s[r] == nxt {
                break;
            }
            r -= 1;
        }
        if l == r {
            break;
        }
        count += 2;
        l += 1;
        r -= 1;
        k -= 1;
        nxt = if nxt == 'R' { 'L' } else { 'R' };
    }
    if k > 0 {
        None
    } else {
        Some(count)
    }
}

#[allow(dead_code)]
struct Scanner<R> {
    reader: BufReader<R>,
    buffer: String,
}
impl<R> Scanner<R>
where
    R: Read,
{
    #[allow(dead_code)]
    fn new(inner: R) -> Scanner<R> {
        let reader = BufReader::new(inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    #[allow(dead_code)]
    fn with_capacity(capacity: usize, inner: R) -> Scanner<R> {
        let reader = BufReader::with_capacity(capacity, inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }

    #[allow(dead_code)]
    fn read_line(&mut self) -> BoxResult<String> {
        self.reader.read_line(&mut self.buffer)?;
        let cloned = self.buffer.trim().to_string();
        self.buffer.clear();
        Ok(cloned)
    }

    #[allow(dead_code)]
    fn read<T>(&mut self) -> BoxResult<T>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed = self.buffer.trim().parse()?;
        self.buffer.clear();
        Ok(parsed)
    }
    #[allow(dead_code)]
    fn read_vector<T>(&mut self) -> BoxResult<Vec<T>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed_vec = self
            .buffer
            .trim()
            .split_whitespace()
            .map(|s| s.parse())
            .collect::<Result<Vec<_>, _>>()?;
        self.buffer.clear();
        Ok(parsed_vec)
    }
    #[allow(dead_code)]
    fn read_matrix<T>(&mut self, lines: usize) -> BoxResult<Vec<Vec<T>>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        let mut parsed_matrix = vec![];
        for _ in 0..lines {
            self.reader.read_line(&mut self.buffer)?;
            parsed_matrix.push(
                self.buffer
                    .trim()
                    .split_whitespace()
                    .map(|s| s.parse())
                    .collect::<Result<Vec<_>, _>>()?,
            );
            self.buffer.clear();
        }
        Ok(parsed_matrix)
    }
    #[allow(dead_code)]
    fn read_chars(&mut self) -> BoxResult<Vec<char>> {
        self.reader.read_line(&mut self.buffer)?;
        let chars = self.buffer.trim().chars().collect::<Vec<_>>();
        self.buffer.clear();
        Ok(chars)
    }
}


Measured memory_bytes: 4352