#[allow(unused_imports)]
use std::cmp::{Ordering};

#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};

#[allow(unused_imports)]
use std::io::{stdin, stdout, BufWriter, Write};

#[allow(unused_imports)]
use std::iter::FromIterator;

#[allow(unused_macros)]
macro_rules! min {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::min($x, min!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! max {
    ($x: expr) => ($x);
    ($x: expr, $($z: expr),+) => {{
        std::cmp::max($x, max!($($z),*))
    }}
}

#[allow(unused_macros)]
macro_rules! get { 
    ([$t: ty]) => { 
        { 
            let mut line = String::new(); 
            stdin().read_line(&mut line).unwrap(); 
            line.split_whitespace().map(|t|t.parse::<$t>().unwrap()).collect::<Vec<_>>()
        }
    };
    ([$t: ty];$n: expr) => {
        (0..$n).map(|_|get!([$t])).collect::<Vec<_>>()
    };
    ($t: ty) => {
        {
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            line.trim().parse::<$t>().unwrap()
        }
    };
    ($($t: ty),*) => {
        { 
            let mut line = String::new();
            stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            ($(iter.next().unwrap().parse::<$t>().unwrap(),)*)
        }
    };
    ($t: ty; $n: expr) => {
        (0..$n).map(|_|get!($t)).collect::<Vec<_>>()
    };
    ($($t: ty),*; $n: expr) => {
        (0..$n).map(|_|get!($($t),*)).collect::<Vec<_>>()
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        #[cfg(debug_assertions)]
        writeln!(&mut std::io::stderr(), concat!("[DEBUG] ", $(stringify!($a), "={:?} "),*), $($a),*).unwrap();
    }
}

const BIG_STACK_SIZE: bool = true;

#[allow(dead_code)]
fn main() {
    use std::thread;
    if BIG_STACK_SIZE {
        thread::Builder::new()
            .stack_size(32 * 1024 * 1024)
            .name("solve".into())
            .spawn(solve)
            .unwrap()
            .join()
            .unwrap();
    } else {
        solve();
    }
}

fn solve() {
    let (n,k) = get!(usize, usize);
    let s = get!(String).chars().collect::<Vec<_>>();

    let mut zflag = false;
    let mut count = 0;
    let mut kat = Vec::new();
    for i in 0..n {
        if s[i] == '0' {
            if !zflag && i>0 {
                kat.push(count);
                count = 0;
            }
            count += 1;
            zflag = true;
        } else {
            if zflag {
                kat.push(count);
                count = 0;
            }
            count += 1;
            zflag = false;
        }
    }
    kat.push(count);


    let mut sums = kat.iter().scan(0, |sum, &e| {
        *sum += e;
        Some(*sum)
    }).collect::<Vec<_>>();
    
    if kat.len() % 2 == 0 {
        if kat.len()/2 <= k {
            println!("{}", n);
            return;
        }
            
    } else {
        if s[0] == '0' {
            if kat.len()/2+1 <= k {
                println!("{}", n);
                return;
            }

        }  else {
            if kat.len()/2 <= k {
                println!("{}", n);
                return;
            }
        }
    }
    if s[0] == '1' {
        sums.insert(0, 0);
    }
    if s[n-1] == '0' {
        sums.push(n);
    }

    let mut mx = sums[2*k-1];
    for i in 0..sums.len() {
        if i % 2 != 0 {
            continue;
        }
        if i+2*k+1 >= sums.len() {
            break;
        }
        mx = max!(mx, sums[i+2*k+1]-sums[i]);
    }
    println!("{}", mx);        
}


Measured memory_bytes: 10620