#include<iostream>
#include<algorithm>
#include <iostream> 
#include <algorithm> 
#include<string>
#include<queue>
#include<utility>
#include<fstream>
#include<queue>
#include<set>
#include<stack>
#include<bits/stdc++.h>
#define ll long long int
#define ull unsigned long long int
#define I(a) scanf("%d",&a)
#define I2(a,b) scanf("%d%d",&a,&b)
#define I3(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define L(a) scanf("%lld",&a)
#define L2(a,b) scanf("%lld%lld",&a,&b)
#define L3(a,b,c) scanf("%lld%lld%lld",&a,&b,&c)
#define PI(a) printf("%d",a)
#define PL(a) printf("%lld",a)
#define PT(t) printf("Case %d: ",t)
#define PB push_back
#define x first
#define y second
#define xx first.first
#define xy first.second
#define yx second.first
#define yy second.second
#define SC scanf
#define PC printf
#define NL printf("\n")
#define SET(a) memset(a,0,sizeof a)
#define SETR(a) memset(a,-1,sizeof a)
#define SZ(a) ((int)a.size())-1
#define f(i,a,b) for(int i=a;i<=b; i++)
#define fr(i,a,b) for(int i=a;i<=b; i++)
#define frr(i,a,b) for(int i=a;i>=b; i--)
#define frv(i,a)  for(int i=0;i<a.size();i++)
#define pi 2.0*acos(0.0)
#define R(a) freopen(a, "r", stdin);
#define W(a) freopen(a, "w", stdout);
#define CB(x) __builtin_popcount(x)
#define STN(a) stringtonumber<ll>(a)
#define lol printf("BUG\n")
#define Endl "\n"
#define mk make_pair
using namespace std;
template <class T> inline T BM(T p, T e, T M)
{
    ll ret = 1;
    for(; e > 0; e >>= 1)
    {
        if(e & 1) ret = (ret * p) % M;
        p = (p * p) % M;
    }
    return (T)ret;
}
template <class T> inline T gcd(T a, T b)
{
    if(b == 0)return a;
    return gcd(b, a % b);
}
template <class T> inline T mdINV(T a, T M)
{
    return BM(a, M - 2, M);
}
template <class T> inline T PW(T p, T e)
{
    ll ret = 1;
    for(; e > 0; e >>= 1)
    {
        if(e & 1) ret = (ret * p);
        p = (p * p);
    }
    return (T)ret;
}
 
 
template <class T>bool ISLEFT(T a, T b, T c)
{
    if(((a.xx - b.xx) * (b.yy - c.yy) - (b.xx - c.xx) * (a.yy - b.yy)) < 0.0)return 1;  //Uporer dike //A,b,c, x okkher ordera sorted
    else return 0;
}
 
 
typedef pair<int,int >P;
//////////////////////////
/////////////////////////

char ar[12][1002];

int main(){

    int n,m,k1;
    I3(n,m,k1);

    for(int i = 1;i<=n;i++){
        SC("%s", ar[i] + 1);
    }
    int l = n-1;
    int DP[1002];
    int an[n+2][m+2];
    int ke[n+2];
    int ans = n * m;
    for(int i = 0;i<(1<<l);i++){
        for(int j = 0;j<=m;j++)DP[j] = n * m;
        int sz = 1;
        for(int j = 0; j<=l;j++){
            ke[j + 1] = sz;
            if((i&(1<<j)))sz++;
        }
  
        SET(an);
        for(int j = 1;j<=m;j++){
            for(int k =1;k<=n;k++)an[k][j] = an[k][j-1];
            for(int k = 1;k<=n;k++){
                if(ar[k][j] == '1'){
                    an[ke[k]][j]++;
                }
            }
            
        }

        DP[0] = sz -1;
        for(int j = 1;j <= m;j++){
            int lo = 1, hi = j;
            int fi = j;
            while(lo <=hi){
                int mid = (lo + hi)/2;
                bool fl = 0;
                for(int k = 1; k<=n;k++){
                    if((an[k][j] - an[k][mid-1]) > k1)fl = 1;
                }
                if(!fl){
                    hi = mid-1;
                    fi = mid;
                }
                else lo = mid + 1;
            }
            bool fl = 0;
            for(int k = 1; k<=n;k++){
                if((an[k][j] - an[k][fi-1])>k1)fl = 1;
            }
            if(fl==0)
            for(int lp = fi; lp<=j;lp++){
                DP[j] = min(DP[lp-1]+1, DP[j]);
            }
         

        }
        ans = min(ans, DP[m]-1);
    }

    cout<<ans<<endl;
    return 0;
}

Measured memory_bytes: 256