#include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;

template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename T>
using dijkstra = priority_queue<T, vector<T>, greater<T>>;

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define fbo find_by_order  // k th index
#define ook order_of_key   // strictly smaller than k
#define PI acos(-1.0)
#define inf 0x3f3f3f3f
#define max_ull 18446744073709551615
#define max_ll 9223372036854775807
#define lead_zero(x) __builtin_clzll(x)
#define trail_zero(x) __builtin_ctzll(x)
#define total_1s(x) __builtin_popcountll(x)
#define first_1(x) __builtin_ffsll(x)
#define log2_(x) __builtin_clz(1) - __builtin_clz(x)
#define isLeap(x) ((x % 400 == 0) || (x % 100 ? x % 4 == 0 : false))
#define QUERY           \
    int test;           \
    scanf("%d", &test); \
    for (int _T = 1; _T <= test; _T++)
#define FAST ios_base::sync_with_stdio(0), cin.tie(0)
#define all(v) v.begin(), v.end()
#define reunique(v) v.resize(std::unique(all(v)) - v.begin())
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pul pair<ull, ull>
#define ff first
#define ss second
#define MERGE(v1, v2, v) merge(all(v1), all(v2), back_inserter(v))
#define MP make_pair
#define EB emplace_back
#define read freopen("input.txt", "r", stdin)
#define write freopen("output.txt", "w", stdout)
#define in_range(v, r, l) upper_bound(all(v), r) - lower_bound(all(v), l)
#define LCM(a, b) (a / __gcd(a, b)) * b;

ll rdn(int y, int m, int d) {
    /* Rata Die day one is 0001-01-01 */
    if (m < 3)
        y--, m += 12;
    return 365 * y + y / 4 - y / 100 + y / 400 + (153 * m - 457) / 5 + d - 306;
}
/* Direction arrays */
/*int dx[] = {1,-1,0,0}, dy[] = {0,0,1,-1};                             */  // 4Direction
/*int dx[] = {1,-1,0,0,1,1,-1,-1}, dy[] = {0,0,1,-1,1,-1,1,-1};         */  // 8Direction
/* int dx[] = {1,-1,1,-1,2,2,-2,-2} , dy[] = {2,2,-2,-2,1,-1,1,-1};     */  // KnightDirection
/* int dx[] = {2,-2,1,1,-1,-1} , dy[] = {0,0,1,-1,1,-1};                */  // HexagonalDirection
/* int day[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; */

string ara[1009];
int barrier[20];
int cnt[20];
int tmp[20];
int main() {
    FAST;
    int n, m, k;
    cin >> n >> m >> k;
    for (int i = 0; i < n; i++) {
        cin >> ara[i];
    }
    int ans = 10000;
    for (int i = 0; i < (1 << (n - 1)); i++) {
        int t = i;
        memset(barrier, 0, sizeof barrier);
        int anstmp = 0;
        for (int j = 1; j < n; j++) {
            barrier[j] = barrier[j - 1];
            if (t & 1) {
                barrier[j]++;
                anstmp++;
            }
            t >>= 1;
        }
        memset(cnt, 0, sizeof cnt);
        for (int l = 0; l < m; l++) {
            bool flagtmp = 1;
            bool flagcnt = 1;
            memset(tmp, 0, sizeof tmp);
            for (int j = 0; j < n; j++) {
                cnt[barrier[j]] += (ara[j][l] - '0');
                tmp[barrier[j]] += (ara[j][l] - '0');

                flagtmp = flagtmp & (tmp[barrier[j]] <= k);
                flagcnt = flagcnt & (cnt[barrier[j]] <= k);
            }
            if (flagtmp == 0) {
                anstmp = 100000;
                break;
            }
            if (flagcnt == 0) {
                anstmp++;
                for (int j = 0; j <= barrier[n - 1]; j++) {
                    cnt[j] = tmp[j];
                }
            }
        }
        ans = min(ans, anstmp);
    }
    cout << ans << "\n";
}


Measured memory_bytes: 256