import java.io.*;
import java.util.*;
public class Main {
    static int [][]a;
    static int n,m,k;
    static int get(int mask ){
        int[]count = new int[n];
        int ans=0;
        for (int i =0;i<m;i++){
            int pre=0;
            int[]nxtc=new int[n];
            for (int j=0;j<n;j++){
                pre+=a[j][i];
                if ((mask&1<<j)!=0||j==n-1){
                    nxtc[j]=pre;
                    pre=0;
                }
            }
            boolean is=false;
            for (int j =0;j<n;j++){
                if (nxtc[j]>k){
                    return n*m;
                }
                if (nxtc[j]+count[j]>k){
                 is=true;
                }
                else count[j]+=nxtc[j];
            }
            if (is){
                count=nxtc;
                ans++;
            }
        }
        return ans;
    }
    public static void main(String[] args) throws IOException, InterruptedException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        n = sc.nextInt();
        m = sc.nextInt();
        k = sc.nextInt();
        a= new int[n][m];
        for (int i =0;i<n;i++){
            char[]s = sc.next().toCharArray();
            for (int j =0;j<m;j++){
                a[i][j]=s[j]-'0';
            }
        }
        int ans=n*m;
        for (int i =0;i<1<<(n-1);i++){
            ans=Math.min(ans,Integer.bitCount(i)+get(i));
        }
        pw.println(ans);
        pw.flush();
    }
    static int gcd(int x,int y){
        if (x==0)
            return y;
        return gcd(y%x,x);
    }
    static class Scanner {
        StringTokenizer st;
        BufferedReader br;

        public Scanner(FileReader r) {
            br = new BufferedReader(r);
        }

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public long nextLong() throws IOException {
            return Long.parseLong(next());
        }

        public String nextLine() throws IOException {
            return br.readLine();
        }

        public double nextDouble() throws IOException {
            String x = next();
            StringBuilder sb = new StringBuilder("0");
            double res = 0, f = 1;
            boolean dec = false, neg = false;
            int start = 0;
            if (x.charAt(0) == '-') {
                neg = true;
                start++;
            }
            for (int i = start; i < x.length(); i++)
                if (x.charAt(i) == '.') {
                    res = Long.parseLong(sb.toString());
                    sb = new StringBuilder("0");
                    dec = true;
                } else {
                    sb.append(x.charAt(i));
                    if (dec)
                        f *= 10;
                }
            res += Long.parseLong(sb.toString()) / f;
            return res * (neg ? -1 : 1);
        }

        public boolean ready() throws IOException {
            return br.ready();
        }
    }

}

Measured memory_bytes: 38064