#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
const int INF = 1e10;
const int MOD = 1e9 + 7;
#define dump(x)                             \
    if (dbg) {                              \
        cerr << #x << " = " << (x) << endl; \
    }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) ((n >> k) & 1) /*nのk bit目*/
template <class T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return 1;
    } else
        return 0;
}
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    } else
        return 0;
}
void Yes(bool flag = true) {
    if (flag)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
}
void No(bool flag = true) {
    Yes(!flag);
}
void YES(bool flag = true) {
    if (flag)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
}
void NO(bool flag = true) {
    YES(!flag);
}
#define pb push_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define P pair<int, int>
//#define V vector<int>
//#define S set<int>
#define itn int
bool dbg = false;

int H, W, K;
string S[20];

void solve() {
    int ans = INF;
    for (int x = 0; x < (1ll << (H - 1)); x++) {
        bool flag2 = false;
        int ANS = __builtin_popcount(x);

        int a[11] = {};
        int c = 0;
        FOR(H) {
            a[i] = c;
            if (x & (1ll << i))
                c++;
        }
        c++;

        int cnt[11] = {};
        FOR(w, 0, W) {
            int flag = true;
            int tmp[11] = {};
            FOR(c) {
                tmp[i] = cnt[i];
            }

            FOR(h, H) {
                tmp[a[h]] += S[h][w];
            }
            FOR(c) {
                //cerr << tmp[i] << " ";
                if (tmp[i] > K) {
                    flag = false;
                }
            }
            //cerr << endl;
            if (flag) {
                FOR(c)
                cnt[i] = tmp[i];
            } else {
                FOR(c)
                cnt[i] = 0;
                FOR(h, H) {
                    cnt[a[h]] += S[h][w];
                }
                ANS++;
            }
            FOR(c)
            if (cnt[i] > K) {
                flag2 = 1;
            }
            if (flag2)
                break;
        }
        if (flag2) {
            continue;
        }
        //cerr << bitset<10>(x) << " : " << ANS << endl;
        chmin(ans, ANS);
    }
    cout << ans << endl;
}

signed main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin >> H >> W >> K;
    FOR(H)
    cin >> S[i];
    FOR(H) {
        for (auto& c : S[i])
            c -= '0';
    }


    solve();
    return 0;
}


Measured memory_bytes: 256