use std::io::Write;
use std::collections::*;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;

fn main() {
    input! {
        n: usize,
        m: usize,
        k: usize,
        s: bytes,
    }
    let mut right = vec![n + 1; n + 2];
    // 0の個数
    let mut sum = vec![0; n + 1];
    for (i, s) in s.iter().enumerate().rev() {
        sum[i] = sum[i + 1];
        right[i] = right[i + 1];
        if *s == b'0' {
            right[i] = i;
            sum[i] += 1;
        }
    }
    let can = |d: usize| -> bool {
        let inf = n + 2;
        let mut dp = vec![[inf; 6]; n + 2];
        dp[0][0] = 0;
        for i in 0..n {
            let src = dp[i];
            for (dp, src) in dp[i + 1].iter_mut().zip(src.iter()) {
                dp.chmin(*src);
            }
            if i + d <= n {
                let need = sum[i] - sum[i + d];
                let pos = right[i + d + 1];
                for (dp, src) in dp[pos][1..].iter_mut().zip(src.iter()) {
                    dp.chmin(*src + need);
                }
            }
        }
        dp[n..].iter().any(|dp| dp[k] <= m)
    };
    if !can(1) {
        println!("-1");
        return;
    }
    let mut ok = 1;
    let mut ng = n + 1;
    while ng - ok > 1 {
        let mid = (ok + ng) / 2;
        if can(mid) {
            ok = mid;
        } else {
            ng = mid;
        }
    }
    println!("{}", ok);
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
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_export]
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_export]
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 ----------
// ---------- begin chmin, chmax ----------
pub trait ChangeMinMax {
    fn chmin(&mut self, x: Self) -> bool;
    fn chmax(&mut self, x: Self) -> bool;
}

impl<T: PartialOrd> ChangeMinMax for T {
    fn chmin(&mut self, x: Self) -> bool {
        *self > x && {
            *self = x;
            true
        }
    }
    fn chmax(&mut self, x: Self) -> bool {
        *self < x && {
            *self = x;
            true
        }
    }
}
// ---------- end chmin, chmax ----------