#pragma GCC optimize(2)
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;

const ll mod = 1e9 + 7;
const int N = 1e3 + 10, M = 1e2 + 30;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const int inf = 0x3f3f3f3f;
const double eps = 1e-8;

#define pi aaos(-1)
#define mk make_pair

char mp[12][N];
int id[N];

int main()
{
    int n, m, w;
    cin >> n >> m >> w;
    for (int i = 0; i < n; i++)
    {
        scanf("%s", mp[i]);
    }
    int ans = n + m;
    for (int i = 0; i < 1 << n; i++)
    {
        int cnt = 0;
        for (int j = 1; j < n; j++)
        {
            if (i >> j & 1)
            {
                id[cnt++] = j;
            }
        }
        if (cnt)
        {
            id[cnt++] = n;
            int ct1[12] = {0}, ct2[12] = {0};
            int flag = 1;
            int tot = 0;
            for (int j = 0; j < m; j++)
            {
                int l = 0;
                int num = 0;
                for (int k = 0; k < n; k++)
                {
                    if (k < id[l])
                    {
                        if (mp[k][j] == '1')
                            num++;
                    }
                    else
                    {
                        if (num > w)
                        {
                            flag = 0;
                            break;
                        }
                        else
                        {
                            ct2[l] = num;
                            num = 0;
                        }
                        if (mp[k][j] == '1')
                            num++;
                        l++;
                    }
                    if (k == n - 1)
                    {
                        if (num > w)
                        {
                            flag = 0;
                            break;
                        }
                        else
                        {
                            ct2[l] = num;
                        }
                    }
                }
                if (!flag)
                    break;
                int f = 1;
                for (int k = 0; k < cnt; k++)
                {
                    if (ct1[k] + ct2[k] <= w)
                        ct1[k] += ct2[k];
                    else
                    {
                        f = 0;
                        break;
                    }
                }
                if (!f)
                {
                    tot++;
                    for (int k = 0; k < cnt; k++)
                        ct1[k] = ct2[k];
                }
            }
            if (flag)
            {
                ans = min(ans, cnt - 1 + tot);
            }
        }
        else
        {
            int sum = 0;
            for (int j = 0; j < m; j++)
            {
                int num = 0;
                for (int k = 0; k < n; k++)
                {
                    if (mp[k][j] == '1')
                    {
                        num++;
                    }
                }
                if (num > w)
                {
                    sum = inf;
                    break;
                }
                else if (sum + num <= w)
                    sum += num;
                else
                {
                    sum = num;
                    cnt++;
                }
            }
            if (sum <= w)
                ans = min(ans, cnt);
        }
    }
    cout << ans << endl;
    return 0;
}

Measured memory_bytes: 256