#include<bits/stdc++.h>
using namespace std;
/*#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
/*template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
*/typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll,ll> pl;
typedef pair<int,int> pii;

#define int ll
#define LOCAL 0
#define dbg(x) cout << #x << " is " << x << "\n"
#define gll(x) scanf("%d",&x)
#define gll2(x,y) scanf("%d%d",&x,&y)
#define gll3(x,y,z) scanf("%d%d%d",&x,&y,&z)
#define gllarr(arr,n) f(i,n) gll(arr[i]);
#define sz(x) ((int)x.size())
#define s(x) sort(x.begin(),x.end())
#define all(v) v.begin(),v.end()
#define rs(v) { s(v) ; r(v) ; }
#define r(v) {reverse(all(v));}
#define pb push_back
#define f(i,n) for(int i=0;i<n;i++)
#define fr(i,n) for(int i=n-1;i>=0;i--)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define repr(i,a,b) for(int i=a;i>=b;i--)

const ll mod = (ll)1e9 + 7;
const ll inf = (ll)1e16;
const ld eps = 1e-12;
const ll N = (int)2e5 + 5;
const ll LOGN = 19;
const ld PI = 3.14159265358979323846;
inline ll mul(ll a, ll b, ll m = mod) { return (ll)(a * b) % m;}
inline ll add(ll a, ll b, ll m = mod) { a += b; if(a >= m) a -= m; if(a < 0) a += m; return a;}
inline ll power(ll a, ll b, ll m = mod) { if(b == 0) return 1; if(b == 1) return (a % m); ll x = power(a, b / 2, m); x = mul(x, x, m); if(b % 2) x = mul(x, a, m); return x;}

int n, m, k;
char a[12][1005];
int preCntByColumn[12][1005];

int getCntByColumn(int num, int L, int R) {
    if(L == 0) return preCntByColumn[num][R];
    return preCntByColumn[num][R] - preCntByColumn[num][L - 1];
}

int getAns(int mask) {
    vector<int> brokenRows;
    brokenRows.pb(-1);
    for(int i = 0; i < n - 1; i++) {
        if(mask & (1 << i)) {
            brokenRows.pb(i);
        }
    }
    brokenRows.pb(n - 1);
    set<int> brokenColumns;
    brokenColumns.insert(-1);
    bool can = true;
    f(i, 12) f(j, 1005) preCntByColumn[i][j]=0;
    for(int j = 0; j < m; j++) {
        for (int i = 0; i < brokenRows.size() - 1; i++) {
            int st_row = brokenRows[i] + 1, fin_row = brokenRows[i + 1];
            int curr = 0;
            for(int tt = st_row; tt <= fin_row; tt++) {
                if(a[tt][j] == '1') curr++;
            }
            if(curr > k) return INT_MAX;
            preCntByColumn[i][j] = curr;
            if(j != 0) preCntByColumn[i][j] += preCntByColumn[i][j - 1];
            int lastBreak = *brokenColumns.rbegin();
            if(getCntByColumn(i, lastBreak + 1, j) > k) brokenColumns.insert(j - 1);
        }
    }
//    if(mask == 2) {
//        cout<<"Print\n";
//        for(auto &it: brokenRows) cout<<it<<' ';
//        cout<<endl;
//
//        for(auto &it: brokenColumns) cout<<it<<' ';
//        cout<<endl;
//    }
    int ret = __builtin_popcount(mask) + brokenColumns.size() - 1;
    return ret;
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    if (LOCAL) {
        freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\input.txt", "r", stdin);
        freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\output.txt", "w", stdout);
    }
    cin>>n>>m>>k;
    f(i, n) {
        string s;
        cin>>s;
        f(j, m) a[i][j] = s[j];
    }
    int ans = INT_MAX;
    f(mask, (1 << (n - 1))) {
        //cout<<mask<<' '<<getAns(mask)<<endl;
        ans = min(ans, getAns(mask));
    }
    cout<<ans;
    return 0;
}

Measured memory_bytes: 384