#include <iostream>
#include <iomanip>
#include <string>
#include <stack>
#include <vector>
#include <complex>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <iterator>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <regex>
#include <limits>
#include <time.h>
#include <cstdint>
using namespace std;
using pii  = pair<int,int>;
using ll=long long;
using ld=long double;
#define pb push_back
#define mp make_pair
#define sc second
#define fr first
#define stpr setprecision
#define cYES cout<<"YES"<<endl
#define cNO cout<<"NO"<<endl
#define cYes cout<<"Yes"<<endl
#define cNo cout<<"No"<<endl
#define rep(i,n) for(ll i=0;i<(n);++i)
#define Rep(i,a,b) for(ll i=(a);i<(b);++i)
#define rrep(i,n) for(ll i=n-1;i>=0;i--)
#define rRep(i,a,b) for(ll i=a;i>=b;i--)
#define crep(i) for(char i='a';i<='z';++i)
#define psortsecond(A,N) sort(A,A+N,[](const pii &a, const pii &b){return a.second<b.second;});
#define ALL(x) (x).begin(),(x).end()
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define endl '\n'
int ctoi(const char c){
  if('0' <= c && c <= '9') return (c-'0');
  return -1;
}
ll gcd(ll a,ll b){return (b == 0 ? a : gcd(b, a%b));}
ll lcm(ll a,ll b){return a*b/gcd(a,b);}
constexpr ll MOD=1000000007;
constexpr ll INF=1000000011;
constexpr ll MOD2=998244353;
constexpr ll LINF = 1001002003004005006ll;
constexpr ld EPS=10e-8;
template <class T, class U> inline bool chmax(T& lhs, const U& rhs) { if (lhs < rhs) { lhs = rhs; return 1; } return 0; }
template <class T, class U> inline bool chmin(T& lhs, const U& rhs) { if (lhs > rhs) { lhs = rhs; return 1; } return 0; }
template<typename T> istream& operator>>(istream& is,vector<T>& v){for(auto&& x:v)is >> x;return is;}
template<typename T,typename U> istream& operator>>(istream& is, pair<T,U>& p){ is >> p.first; is >> p.second; return is;}
template<typename T,typename U> ostream& operator>>(ostream& os, const pair<T,U>& p){ os << p.first << ' ' << p.second; return os;}
template<class T> ostream& operator<<(ostream& os, vector<T>& v){
  for(auto i=begin(v); i != end(v); ++i){
    if(i !=begin(v)) os << ' ';
    os << *i;
  }
  return os;
}

ll  H,W,K;
string S[15];
ll coun[15][1007];
ll C[1007][15];
ll P[15];
ll dp[1007][1007];

int main(){
  cin >> H  >> W >> K;
  rep(i,H){
    cin >> S[i];
  }
  // rep(i,H){
  //   rep(j,W){
  //     ll X=ctoi(S[i][j]);
  //     if(j==0){
  //       coun[i][j+1]=X;
  //     }
  //     else{
  //       coun[i][j+1]=coun[i][j]+X;
  //     }
  //   }
  // }
  ll ans=LINF;
  rep (bit,1<<(H-1)) {  // 0~2^N-1 までのbit 全探索
    ll cut=0;
    rep (j,(H-1)){
      if (bit & (1<<j)) { // i が bit に入るかどうか
        cut++;
      }
    }
    rep(i,H+1){
      rep(k,1001){
      C[k][i]=0;
      }
    }
    ll handan=0;
    Rep(i,1,W+1){
      ll maime=0;
      handan=0;
      rep(j,H){
        P[j]=0;
      }
      rep (j,H){
        if (j!=0 &&  bit & (1<<(j-1))) { // i が bit に入るかどうか
          if(C[i][maime]>K){
            handan=1;
            if(C[i][maime]-C[i-1][maime]>K){
              handan=2;
              break;
            }
          }
          maime++;
        }
        C[i][maime]+=ctoi(S[j][i-1]);
        P[maime]+=ctoi(S[j][i-1]);
      }

      if(C[i][maime]>K){
        handan=1;
        if(C[i][maime]-C[i-1][maime]>K){
          handan=2;
        }
      }

      if(handan==2){
        cut=LINF;
        break;
      }

      if(handan==1){
        cut++;
        rep(j,H){
          C[i+1][j]=P[j];
        }
      }

      if(handan==0){
        rep(j,H){
          C[i+1][j]=C[i][j];
        }
      }
    }
    ans=min(ans,cut);
  }
  cout << ans << endl;
}


Measured memory_bytes: 384