// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------

fn run() {
    input! {
        n: usize,
        k: usize,
        s: bytes,
    }
    let mut cnt = vec![0; n + k + 1];
    for (i, &c) in s.iter().enumerate() {
        if c == b'x' {
            cnt[i + 1] = 1;
        }
    }
    for i in (0..n).rev() {
        cnt[i] += cnt[i + 1];
    }
    let mut right = vec![];
    for i in 0..n {
        if i > 0 && s[i - 1] == b'x' {
            continue;
        }
        let w = k - (cnt[i + 1] - cnt[i + 1 + k]);
        right.push(w);
    }
    let n = right.len();
    let mut dp = vec![false; n];
    let mut lose = n + k + 1;
    for (i, &r) in right.iter().enumerate().rev() {
        if lose <= i + r {
            dp[i] = true;
        } else {
            lose = i;
        }
    }
    println!("{}", dp.iter().position(|p| !*p).unwrap());
}

fn main() {
    run();
}