//  ____            _                  _                       _       _
// |  _ \ _   _ ___| |_    ___ _ __   | |_ ___ _ __ ___  _ __ | | __ _| |_ ___
// | |_) | | | / __| __|  / __| '_ \  | __/ _ \ '_ ` _ \| '_ \| |/ _` | __/ _ \
// |  _ <| |_| \__ \ |_  | (__| |_) | | ||  __/ | | | | | |_) | | (_| | ||  __/
// |_| \_\\__,_|___/\__|  \___| .__/___\__\___|_| |_| |_| .__/|_|\__,_|\__\___|
//                            |_| |_____|               |_|

//https://github.com/manta1130/Competitive_Programming_Template_Rust

#[macro_use]
mod input {

    use std;
    use std::io;

    const SPLIT_DELIMITER: char = ' ';

    #[macro_export]
    #[allow(unused_macros)]
    macro_rules! input {
    ( $($x:expr ),*) => {
        {
            let temp_str = input_line_str();
            let mut split_result_iter = temp_str.split_whitespace();
                $(
                let buf_split_result = split_result_iter.next();
                let buf_split_result = buf_split_result.unwrap();
                    ($x) = buf_split_result.parse().unwrap();
                )*
        }
    };
}

    #[allow(dead_code)]
    pub fn input_line_str() -> String {
        let mut s = String::new();
        io::stdin().read_line(&mut s).unwrap();
        s.trim().to_string()
    }

    #[allow(dead_code)]
    pub fn p<T>(t: T)
    where
        T: std::fmt::Display,
    {
        println!("{}", t);
    }

    #[allow(dead_code)]
    pub fn input_vector2d<T>(line: usize) -> Vec<Vec<T>>
    where
        T: std::str::FromStr,
    {
        let mut v: Vec<Vec<T>> = Vec::new();

        for _ in 0..line {
            let vec_line = input_vector();
            v.push(vec_line);
        }
        v
    }

    #[allow(dead_code)]
    pub fn input_vector<T>() -> Vec<T>
    where
        T: std::str::FromStr,
    {
        let mut v: Vec<T> = Vec::new();

        let s = input_line_str();
        let split_result = s.split(SPLIT_DELIMITER);
        for z in split_result {
            let buf = match z.parse() {
                Ok(r) => r,
                Err(_) => panic!("Parse Error"),
            };
            v.push(buf);
        }
        v
    }

    #[allow(dead_code)]
    pub fn input_vector_row<T>(n: usize) -> Vec<T>
    where
        T: std::str::FromStr,
    {
        let mut v = Vec::with_capacity(n);
        for _ in 0..n {
            let buf = match input_line_str().parse() {
                Ok(r) => r,
                Err(_) => panic!("Parse Error"),
            };
            v.push(buf);
        }
        v
    }

    pub trait ToCharVec {
        fn to_charvec(&self) -> Vec<char>;
    }

    impl ToCharVec for String {
        fn to_charvec(&self) -> Vec<char> {
            self.to_string().chars().collect::<Vec<_>>()
        }
    }
}

use input::*;

fn main() {
    let (h, w, m): (usize, usize, usize);
    input!(h, w, m);
    let mut v = vec![];
    for _ in 0..h {
        let s = input_line_str().to_charvec();
        let mut buf = vec![];
        for i in s {
            if i == '0' {
                buf.push(false);
            } else {
                buf.push(true);
            }
        }
        v.push(buf);
    }

    let mut ans = 999999999999_usize;
    for i in 0..2_usize.pow(h as u32 - 1) {
        let mut hinfo = vec![0; h];
        for j in 0..h - 1 {
            if (i >> j) & 1 == 1 {
                hinfo[j + 1] = hinfo[j] + 1;
            } else {
                hinfo[j + 1] = hinfo[j];
            }
        }

        let mut white = vec![0; h];
        let mut buf = *hinfo.iter().max().unwrap();
        let mut j = 0;
        let mut impossible = false;
        let mut first = true;
        while j < w {
            let mut flag = false;
            let mut k = 0;
            while k < h {
                if v[k][j] {
                    white[hinfo[k]] += 1;
                    if white[hinfo[k]] > m {
                        if first {
                            impossible = true;
                        }
                        buf += 1;
                        flag = true;
                    }
                }
                k += 1;
                if flag || impossible {
                    break;
                }
            }
            if impossible {
                break;
            }
            if flag {
                for z in 0..white.len() {
                    white[z] = 0;
                }
                first = true;
                continue;
            }
            j += 1;
            first = false;
        }
        if impossible {
            continue;
        }
        //println!("{:?}", hinfo);
        //println!("{:?}", white);
        //println!("{}", buf);
        ans = std::cmp::min(ans, buf);
    }
    println!("{}", ans);
}


Measured memory_bytes: 4352