using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
static class Program{
	const int mod=(int)1e9+7;
	const double eps=1e-11;
	static void Main(){
		Sc sc=new Sc();
		var s=sc.Ia;
		s[1]++;
		var h=new int[s[0]+1][];
		var w=new int[s[0]+1][];
		h[0]=new int[s[1]+1];
		w[0]=new int[s[1]+1];
		for(int i = 1;i<=s[0];i++) {
			var e=" "+sc.S+"0";
			h[i]=new int[s[1]+1];
			w[i]=new int[s[1]+1];
			for(int j = 1;j<=s[1];j++) {
				h[i][j]=w[i][j]=e[j]-'0';
			}
		}
		for(int i=1;i<=s[0];i++){
			for(int j=1;j<=s[1];j++){w[i][j]+=w[i][j-1];}
		}
		for(int i=1;i<=s[1];i++){
			for(int j=1;j<=s[0];j++){w[j][i]+=w[j-1][i];}
		}
		int m=1<<(s[0]-1),ans=int.MaxValue;
		for(int i = 0;i<m;i++) {
			var t=Binary(i,s[0]-1)+'1';
			int g=1,z=bits(i);
			for(int l = 1;l<=s[1];l++) {
				int p=0;
				for(int j = 1,k=1;j<=t.Length;j++) {
					if(t[j-1]=='1'){
						p=Max(p,w[j][l]+w[k-1][g-1]-w[j][g-1]-w[k-1][l]);
						k=j+1;
					}
				}
				if(p>s[2]){
					if(g==l){
						z=int.MaxValue;
						break;
					}
					z++;
					g=l;
					l--;
				}
			}
			ans=Min(ans,z);
		}
		Console.WriteLine("{0}",ans);
	}
	static string Binary(long a,int b){
		string s=Convert.ToString(a,2);
		return (b>s.Length?new string('0',b-s.Length):"")+s;
	}
	static int bits(long bits){
		bits=(bits&0x55555555)+(bits>>1&0x55555555);
		bits=(bits&0x33333333)+(bits>>2&0x33333333);
		bits=(bits&0x0f0f0f0f)+(bits>>4&0x0f0f0f0f);
		bits=(bits&0x00ff00ff)+(bits>>8&0x00ff00ff);
		return (int)((bits&0x0000ffff)+(bits>>16&0x0000ffff));
	}
}
public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public object[] Oa{get{return Console.ReadLine().Split();}}
	public int[] Ia2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),int.Parse);}}
	public int[] Ia3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),int.Parse);}
	public int[] Ia3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public long[] La3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),long.Parse);}
	public long[] La3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),long.Parse);}
	public double[] Da2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),double.Parse);}}
	public double[] Da3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),double.Parse);}
	public double[] Da3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),double.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Console.ReadLine().Split());}return a;}
}

Measured memory_bytes: 13396