#include <bits/stdc++.h>
#include <ext/rope>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//#define int long long
#define pb push_back
#define x first
#define y second
#define mk(a,b) make_pair(a,b)
#define rr return 0
#define sqr(a) ((a)*(a))
#define all(a) (a).begin(), (a).end()
#define sz(a) (int)(a).size()

using namespace std;
using namespace __gnu_cxx;
using namespace __gnu_pbds;

using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

template<class value, class cmp = less<value> >
using ordered_set = tree<value, null_type, cmp, rb_tree_tag, tree_order_statistics_node_update>;
template<class value, class cmp = less_equal<value> >
using ordered_multiset = tree<value, null_type, cmp, rb_tree_tag, tree_order_statistics_node_update>;
template<class key, class value, class cmp = less<key> >
using ordered_map = tree<key, value, cmp, rb_tree_tag, tree_order_statistics_node_update>;

/// find_by_order()
/// order_of_key()
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int randll(int l = INT_MIN, int r = INT_MAX) {
    return uniform_int_distribution<int>(l, r)(rng);
}
const int INF = 1e9, MOD = 1e9 + 7; /// think
const ll LINF = 1e18;


const int dx[] = {0, 0, 1, -1}, dy[] = {1, -1, 0, 0};
inline bool inside (int x, int y, int n, int m) {
    return 0 <= x && 0 <= y && x < n && y < m;
}

template<class T> bool umin (T &a, T b) {return a > b ? (a = b, true) : false; }
template<class T> bool umax (T &a, T b) {return a < b ? (a = b, true) : false; }

main()
{
    ios::sync_with_stdio(0);
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n, m, k;
    cin >> n >> m >> k;
    vector <string> a(n);
    for (auto &i : a) cin >> i;
    int ans = INF;
    for (int i = 0; i < (1 << (n - 1)); i++) {
        int res = 0;
        vector <vector<int> > have;
        vector <int> cur(m);
        for (int j = 0; j < n - 1; j++) {
            for (int i1 = 0; i1 < m; i1++) {
                cur[i1] += a[j][i1] - '0';
            }
            if (i & (1 << j)) {
                ++res;
                have.pb(cur);
                cur.assign(m, 0);
            }
        }
        for (int i1 = 0; i1 < m; i1++) {
            cur[i1] += a[n - 1][i1] - '0';
        }
        have.pb(cur);
        int N = sz(have);
        vector <int> now (N);
        bool ok = true;
        for (int j = 0; j < m; j++) {
            bool cut = false;
            for (int i1 = 0; i1 < N; i1++) {
                if (have[i1][j] > k) {
                    ok = false;
                    break;
                }
                if (now[i1] + have[i1][j] > k) {
                    cut = true;
                    break;
                }
            }
            if (cut) {
                ++res;
                for (int i1 = 0; i1 < N; i1++) {
                    now[i1] = 0;
                }
            }
            for (int i1 = 0; i1 < N; i1++) {
                now[i1] += have[i1][j];
            }
        }
        if (ok) {
            umin(ans, res);
        }
    }
    cout << ans << '\n';
}


Measured memory_bytes: 3720