#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using VI = vector<int>;
using VL = vector<ll>;
using loop = int;
template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;
#define FOR(i,a,n) for(loop (i)=(a);(i)<(n);++(i))
#define eFOR(i,a,n) for(loop (i)=(a);(i)<=(n);++(i))
#define rFOR(i,a,n) for(loop (i)=(n)-1;(i)>=(a);--(i))
#define erFOR(i,a,n) for(loop (i)=(n);(i)>=(a);--(i))
#define each(i, a) for(auto &i : a)
#define SORT(i) sort((i).begin(),(i).end())
#define rSORT(i,a) sort((i).begin(),(i).end(),(a))
#define all(i) (i).begin(),(i).end()
#define out(y,x) ((y) < 0 || h <= (y) || (x) < 0 || w <= (x))
#define line cout << "------------------------\n" 
#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")
#define stop system("pause") //comment out this on AOJ.
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 60;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr ld pi = 3.1415926535897932;
template<class T>inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; }return false; }
template<class T>inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; }return false; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T>inline istream& operator>>(istream& is, vector<T>& v) { for (auto& elemnt : v)is >> elemnt; return is; }
template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }
template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }
template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }

vector<VI> acc;
int sum(int y1, int x1, int y2, int x2) {
    int ret = acc[y2][x2];
    if (0 < y1)ret -= acc[y1 - 1][x2];
    if (0 < x1)ret -= acc[y2][x1 - 1];
    if (0 < y1 && 0 < x1)ret += acc[y1 - 1][x1 - 1];
    return ret;
}

int main() {
    init();

    int h, w, k; cin >> h >> w >> k;
    vector<string> s(h); cin >> s;

    acc = vec<int>(h, w);
    FOR(i, 0, h)FOR(j, 0, w)if (s[i][j] == '1')++acc[i][j];
    FOR(i, 0, h)FOR(j, 1, w)acc[i][j] += acc[i][j - 1];
    FOR(i, 1, h)FOR(j, 0, w)acc[i][j] += acc[i - 1][j];

    int ans = INF;
    FOR(bit, 0, 1 << (h - 1)) {
        int cnt = 0;
        VI a = { -1 };
        FOR(i, 0, h - 1)if (bit & (1 << i)) {
            ++cnt;
            a.push_back(i);
        }
        a.push_back(h - 1);
        int bef = 0;
        bool ng = false;
        FOR(j, 0, w) {
            FOR(i, 1, a.size()) {
                if (k < sum(a[i - 1] + 1, bef, a[i], j)) {
                    ++cnt;
                    bef = j;
                    FOR(p, 1, a.size())if (k < sum(a[p - 1] + 1, bef, a[p], j)) {
                        ng = true;
                    }
                    break;
                }
            }
        }
        if (ng)continue;
        chmin(ans, cnt);
    }

    cout << ans << "\n";
}


Measured memory_bytes: 384