#pragma GCC optimize ("Ofast")
#include<bits/stdc++.h>
using namespace std;
template<class S, class T> inline S max_L(S a,T b){
  return a>=b?a:b;
}
inline int my_getchar_unlocked(){
  static char buf[1048576];
  static int s = 1048576;
  static int e = 1048576;
  if(s == e && e == 1048576){
    e = fread_unlocked(buf, 1, 1048576, stdin);
    s = 0;
  }
  if(s == e){
    return EOF;
  }
  return buf[s++];
}
inline void rd(int &x){
  int k;
  int m=0;
  x=0;
  for(;;){
    k = my_getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = my_getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
inline void rd(char &c){
  int i;
  for(;;){
    i = my_getchar_unlocked();
    if(i!=' '&&i!='\n'&&i!='\r'&&i!='\t'&&i!=EOF){
      break;
    }
  }
  c = i;
}
inline int rd(char c[]){
  int i;
  int sz = 0;
  for(;;){
    i = my_getchar_unlocked();
    if(i!=' '&&i!='\n'&&i!='\r'&&i!='\t'&&i!=EOF){
      break;
    }
  }
  c[sz++] = i;
  for(;;){
    i = my_getchar_unlocked();
    if(i==' '||i=='\n'||i=='\r'||i=='\t'||i==EOF){
      break;
    }
    c[sz++] = i;
  }
  c[sz]='\0';
  return sz;
}
struct MY_WRITER{
  char buf[1048576];
  int s;
  int e;
  MY_WRITER(){
    s = 0;
    e = 1048576;
  }
  ~MY_WRITER(){
    if(s){
      fwrite_unlocked(buf, 1, s, stdout);
    }
  }
}
;
MY_WRITER MY_WRITER_VAR;
void my_putchar_unlocked(int a){
  if(MY_WRITER_VAR.s == MY_WRITER_VAR.e){
    fwrite_unlocked(MY_WRITER_VAR.buf, 1, MY_WRITER_VAR.s, stdout);
    MY_WRITER_VAR.s = 0;
  }
  MY_WRITER_VAR.buf[MY_WRITER_VAR.s++] = a;
}
inline void wt_L(char a){
  my_putchar_unlocked(a);
}
inline void wt_L(int x){
  int s=0;
  int m=0;
  char f[10];
  if(x<0){
    m=1;
    x=-x;
  }
  while(x){
    f[s++]=x%10;
    x/=10;
  }
  if(!s){
    f[s++]=0;
  }
  if(m){
    my_putchar_unlocked('-');
  }
  while(s--){
    my_putchar_unlocked(f[s]+'0');
  }
}
template<class S, class T> inline S chmin(S &a, T b){
  if(a>b){
    a=b;
  }
  return a;
}
int X;
int Y;
int K;
char S[10][1002];
int d[10];
int cnt[10];
int sz;
int main(){
  int i, mask;
  int res = 1073709056;
  int tmp;
  rd(X);
  rd(Y);
  rd(K);
  {
    int Lj4PdHRW;
    for(Lj4PdHRW=(0);Lj4PdHRW<(X);Lj4PdHRW++){
      rd(S[Lj4PdHRW]);
    }
  }
  for(i=(0);i<(X);i++){
    int j;
    for(j=(0);j<(Y);j++){
      S[i][j] -= '0';
    }
  }
  for(mask=(0);mask<(1<<(X-1));mask++){
    int j;
    sz = 0;
    for(i=(0);i<(X);i++){
      d[i] = sz;
      if(mask&(1<<i)){
        sz++;
      }
    }
    sz++;
    for(i=(0);i<(sz);i++){
      cnt[i] = 0;
    }
    tmp = sz - 1;
    for(j=(0);j<(Y);j++){
      for(i=(0);i<(X);i++){
        cnt[d[i]] += S[i][j];
      }
      int YREPHmFM;
      int jZyWAPpY;
      if(sz==0){
        jZyWAPpY = 0;
      }
      else{
        jZyWAPpY = cnt[0];
        for(YREPHmFM=(1);YREPHmFM<(sz);YREPHmFM++){
          jZyWAPpY = max_L(jZyWAPpY, cnt[YREPHmFM]);
        }
      }
      if(jZyWAPpY> K){
        tmp++;
        for(i=(0);i<(sz);i++){
          cnt[i] = 0;
        }
        for(i=(0);i<(X);i++){
          cnt[d[i]] += S[i][j];
        }
      }
      int BUotOFBp;
      int Q5rsz4fz;
      if(sz==0){
        Q5rsz4fz = 0;
      }
      else{
        Q5rsz4fz = cnt[0];
        for(BUotOFBp=(1);BUotOFBp<(sz);BUotOFBp++){
          Q5rsz4fz = max_L(Q5rsz4fz, cnt[BUotOFBp]);
        }
      }
      if(Q5rsz4fz> K){
        tmp = 1073709056;
        break;
      }
    }
    chmin(res, tmp);
  }
  wt_L(res);
  wt_L('\n');
  return 0;
}
// cLay varsion 20200321-1

// --- original code ---
// int X, Y, K;
// char S[10][1002];
// int d[10], cnt[10], sz;
// {
//   int res = int_inf, tmp;
//   rd(X,Y,K,S(X));
//   rep(i,X) rep(j,Y) S[i][j] -= '0';
//   rep(mask,1<<(X-1)){
//     sz = 0;
//     rep(i,X){
//       d[i] = sz;
//       if(mask&(1<<i)) sz++;
//     }
//     sz++;
//     rep(i,sz) cnt[i] = 0;
//     tmp = sz - 1;
// 
//     rep(j,Y){
//       rep(i,X) cnt[d[i]] += S[i][j];
//       if(max(cnt(sz)) > K){
//         tmp++;
//         rep(i,sz) cnt[i] = 0;
//         rep(i,X) cnt[d[i]] += S[i][j];
//       }
//       if(max(cnt(sz)) > K){
//         tmp = int_inf;
//         break;
//       }
//     }
//     res <?= tmp;
//   }
//   wt(res);
// }


Measured memory_bytes: 256