#include "vector"
#include "set"
#include "map"
#include "unordered_set"
#include "unordered_map"
#include "string"
#include "iostream"
#include "algorithm"
#include "queue"

using namespace std;

#define ll long long
#define INF 2e9
#define INF2 4611686018427387904
//#define MOD 1000000007
#define MOD 998244353
#define MAX_SIZE 1000000000

typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;

template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) { bool first = true; for (const auto& j: v) { if (!first) { os << " "; } first = false; os <<j; } os << "\n"; return os; }
template<typename T>
istream& operator>>(istream& is, vector<T>& v) { for (auto& elem : v) { is >> elem; } return is; }

vector<ll> f;
void set_f(int n) { f.resize(n+1); f[0] = 1; for (int i=1; i<= n; i++) { f[i] = (f[i-1] * i) % MOD;} }
ll nod(ll a, ll b) { if (b == 0) { return a; } else { return nod(b, a % b); } }
ll pw(ll x, ll n, ll m=MOD) { if (n == 0) { return 1;} if (n%2 == 0) { return pw((x*x) % m, n/2, m); } return (pw(x, n-1, m) * x) % m; }
ll dv(ll a, ll b) { return (a * pw(b, MOD - 2)) % MOD; }
ll c_n_k(int n, int k) { if (k > n) { return 0; } if (k < 0) { return 0; } return dv(dv(f[n], f[k]), f[n-k]); }

void solve() {
    int n, m, k;
    cin >> n >> m >> k;

    vector<string> s(n);
    cin >> s;

    vector<vi> pref(n, vi(m+1, 0));
    for (int j=0; j<n; j++) {
        for (int i=1; i<=m; i++) {
            pref[j][i] = pref[j][i-1];
            if (s[j][i-1]=='1') {
                pref[j][i]++;
            }
        }
    }

    int ans = INF;
    for (int i=0; i < 1 << (n-1); i++) {
        int cur = 0;

        vi b(n);
        for (int j=0; j < n; j++) {
            b[j] = cur;
            if (i & (1 << j)) {
                cur++;
            }
        }
        int len = cur+1;

        vi c(len, 0);

        for (int j=0; j<m; j++) {
            for (int ii=0; ii<n; ii++) {
                if (s[ii][j] == '1') {
                    c[b[ii]]++;
                }
            }

            bool can = true;
            for (int ii=0; ii<len; ii++) {
                if (c[ii] > k) {
                    can = false;
                    break;
                }
            }

            if (!can) {
                cur++;

                c.assign(len, 0);
                for (int ii=0; ii<n; ii++) {
                    if (s[ii][j] == '1') {
                        c[b[ii]]++;
                    }
                }


                bool can = true;
                for (int ii=0; ii<len; ii++) {
                    if (c[ii] > k) {
                        can = false;
                        break;
                    }
                }

                if (!can) {
                    cur = INF;
                    break;
                }
            }
        }

        ans = min(cur, ans);
    }

    cout << ans;
}

int main() {
    ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);

    if (0) {
        int tests;
        cin >> tests;
        for (int t = 1; t <= tests; t++) {
            //cout << "Case #" << t << ": ";
            solve();
            //cout << "\n";
        }
    } else {
        solve();
        cout << endl;
    }

    return 0;
}


Measured memory_bytes: 384