using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;

namespace A
{
    class StartingPoint
    {
        static void Main(string[] args)
        {
            if (args?.Any() == true)
            {
                var assembly = Assembly.GetEntryAssembly();
                var resourceName = "AtCoderCSharp.In.txt";
                var stream = assembly.GetManifestResourceStream(resourceName);
                var streamReader = new StreamReader(stream, Encoding.UTF8);
                var str = streamReader.ReadToEnd();
                var textReader = new StringReader(str);
                Console.SetIn(textReader);
            }

            try
            {
                foreach (var s in new Program().Solve())
                {
                    Console.WriteLine(s);
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
                if (args?.Any() != true)
                    throw e;
            }

            if (args?.Any() == true)
                Console.ReadKey();
        }
    }

    class Program
    {
        public List<int> ScanInts(int count) => Enumerable.Range(0, count).Select(_ => ScanInt).ToList();
        public List<int> ScanInts(long count) => ScanInts((int)count);
        public List<long> ScanLongs(int count) => Enumerable.Range(0, count).Select(_ => Scan).ToList();
        public List<long> ScanLongs(long count) => ScanLongs((int)count);
        public int ScanInt => int.Parse(Str);
        public long Scan => long.Parse(Str);
        public double ScanDouble => (double)Scan;

        StringBuilder sb = new StringBuilder();

        public string Str => ScanStr();
        public string ScanStr()
        {
            sb.Clear();

            int r = 0;
            bool? b = null;
            do
            {
                r = Console.Read();
                b = IsBreak(r);
            } while (b == true);

            if (b == null)
                throw new Exception("input error: unexpected end of stream");

            do
            {
                sb.Append((char)r);
                r = Console.Read();
                b = IsBreak(r);
            } while (b == false);

            return sb.ToString();
        }

        bool? IsBreak(int c)
        {
            switch (c)
            {
                case -1:
                    return null;
                case (int)' ':
                case (int)'\n':
                case (int)'\r':
                    return true;
                default:
                    return false;
            }
        }

        public IEnumerable<int> Loop(int count) => Enumerable.Range(0, count);
        public IEnumerable<int> Loop(int from, int to) => Enumerable.Range(from, to - from + 1);

        public IEnumerable<long> Loop(long count) => Loop(0, count - 1);
        public IEnumerable<long> Loop(long from, long to)
        {
            for (long i = from; i <= to; i++)
                yield return i;
        }

        public string YesNo(bool isYes) => isYes ? "Yes" : "No";

        public HashSet<T> ToHashSet<T>(IEnumerable<T> ts) => new HashSet<T>(ts);

        List<string> s;
        int k;

        int Slv(int div)
        {
            var b = new List<int>();
            b.Add(0);

            var d = 0;
            while (div > 0)
            {
                d++;
                if (div % 2 == 1)
                    b.Add(d);

                div /= 2;
            }

            b.Add(s.Count);

            var wh = Enumerable.Range(0, b.Count - 1).Select(x => 0).ToArray();
            var res = 0;
            var pointer = 0;
            var left = 0;

            while (pointer < s[0].Length)
            {
                for (int i = 0; i < b.Count - 1; i++)
                {
                    for (int j = b[i]; j < b[i + 1]; j++)
                    {
                        //Console.WriteLine(j + " " + pointer);
                        if (s[j][pointer] == '1')
                            wh[i]++;
                    }

                }

                if (wh.All(x => x <= k))
                {
                    pointer++;
                }
                else if (left != pointer)
                {
                    left = pointer;
                    res++;
                    wh = Enumerable.Range(0, b.Count - 1).Select(x => 0).ToArray();
                }
                else
                {
                    return int.MaxValue;
                }
            }

            return res + b.Count - 2;

        }

        public IEnumerable<string> Solve()
        {
            var h = ScanInt;
            var w = ScanInt;
            k = ScanInt;
            s = new List<string>();


            foreach (var i in Loop(h))
            {
                var x = ScanStr();
                s.Add(x);
            }

            var res = Enumerable.Range(0, 1 << (h - 1)).Min(x => Slv(x));


            yield return res.ToString();
        }
    }
}

Measured memory_bytes: 17468