#define LOCAL
#define _USE_MATH_DEFINES
#include <array>
#include <cassert>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <vector>
#include <queue>
#include <stack>
#include <list>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <algorithm>
#include <complex>
#include <cmath>
#include <numeric>
#include <bitset>
#include <functional>
#include <random>
#include <ctime>

using namespace std;

template <typename A, typename B>
ostream& operator <<(ostream& out, const pair<A, B>& a) {
  out << "(" << a.first << "," << a.second << ")";
  return out;
}
template <typename T, size_t N>
ostream& operator <<(ostream& out, const array<T, N>& a) {
  out << "["; bool first = true;
  for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]";
  return out;
}
template <typename T>
ostream& operator <<(ostream& out, const vector<T>& a) {
  out << "["; bool first = true;
  for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]";
  return out;
}
template <typename T, class Cmp>
ostream& operator <<(ostream& out, const set<T, Cmp>& a) {
  out << "{"; bool first = true;
  for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "}";
  return out;
}
template <typename U, typename T, class Cmp>
ostream& operator <<(ostream& out, const map<U, T, Cmp>& a) {
  out << "{"; bool first = true;
  for (auto& p : a) { out << (first ? "" : ", "); out << p.first << ":" << p.second; first = 0;} out << "}";
  return out;
}
#ifdef LOCAL
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...) 42
#endif
template <typename Arg1>
void __f(const char* name, Arg1&& arg1){
  cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args){
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << ": " << arg1 << " |";
  __f(comma + 1, args...);
}

typedef long long int64;
typedef pair<int, int> ii;
const int INF = 1 << 29;
const int MOD = 1e9 + 7;
mt19937 mrand(random_device{}());
int rnd(int x) { return mrand() % x; }

struct fast_ios {
  fast_ios() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
  };
} fast_ios_;

const int N = 10;
const int M = 1e3 + 10;
char s[N][M];
int n, m, k;
int best;
vector<int> a;

int solve() {
  int len = a.size();
  vector<vector<int>> b(len, vector<int>(m));
  int offset = 0;
  for (int i = 0; i < len; ++i) {
    for (int j = 0; j < m; ++j) {
      for (int u = 0; u < a[i]; ++u) {
        b[i][j] += s[offset + u][j] - '0';
      }
    }
    offset += a[i];
  }
  vector<int> sum(len);
  int ret = 0;
  for (int i = 0, j; i < m; i = j) {
    fill(sum.begin(), sum.end(), 0);
    for (j = i; j < m; ++j) {
      bool found = false;
      for (int u = 0; u < len; ++u) {
        sum[u] += b[u][j];
        if (sum[u] > k) found = true;
      }
      if (found) break;
    }
    if (j == i) return INF;
    ++ret;
  }
  return ret;
}

void search(int pos) {
  if (pos == n) {
    int cur = solve();
    best = min(best, cur + (int)a.size() - 2);
    return;
  }
  for (int i = 1; pos + i <= n; ++i) {
    a.push_back(i);
    search(pos + i);
    a.pop_back();
  }
}

int main() {
  scanf("%d%d%d", &n, &m, &k);
  for (int i = 0; i < n; ++i) {
    scanf("%s", s[i]);
  }
  best = INF;
  search(0);
  printf("%d\n", best);
  return 0;
}


Measured memory_bytes: 384