/*
Author : N_o_o_B
Created : March 22 2020 17:47:37 
*/
#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;
*/
#define TRACE
#ifdef TRACE
#define trace(...) { cerr<<"[ "; __trace__(#__VA_ARGS__, __VA_ARGS__);}
#undef endl
template <typename Arg1,typename Arg2>
ostream& operator << (ostream& out, const pair<Arg1,Arg2> &x) {
    return out<<"("<<x.first<<","<<x.second<<")";
}
 
template <typename Arg1>
ostream& operator << (ostream& out, const vector<Arg1> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1>
ostream& operator << (ostream& out, const set<Arg1> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1,typename Arg2>
ostream& operator << (ostream& out, const map<Arg1,Arg2> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1>
void __trace__(const string name, Arg1&& arg1){
    cerr << name << " : " << arg1 << " ] " << endl;
}
 
template <typename Arg1, typename... Args>
void __trace__(const string names, Arg1&& arg1, Args&&... args){
    const string name = names.substr(0,names.find(','));
    cerr<<name<<" : "<<arg1<<" | ";
    __trace__(names.substr(1+(int)name.size()), args...);
}
#else
    #define trace(args...)
#endif
 
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pair<int,int>> vii;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<pair<ll,ll>> vll;
typedef vector<vl> vvl;
//typedef tree<pii, null_type, less<pii>, rb_tree_tag, tree_order_statistics_node_update> oset;
#define fori(i,n) for(int i=0;i<n;i++)
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define repd(i,a,b) for(int i=a;i>=b;i--)
#define ford(i,n)  for(int i=n-1;i>=0;i--)
#define trav(x,a) for(auto& x:a)
#define all(x) x.begin(),x.end()
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define fi first
#define se second
clock_t time_p=clock();
void time_taken()
{
    time_p=clock()-time_p;
    cerr<<"Time Taken : "<<(float)(time_p)/CLOCKS_PER_SEC<<"\n";
}
//const ll mod=998244353;
const ll mod=1e9+7;
const ll INF=1e18;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);cout.tie(NULL);
    cout.precision(12);cout << fixed;

    int n,m,k;
    cin >> n >> m >> k;
    vector<string> a(n);
    fori(i,n) cin >> a[i];
    ll ans = INF;
    fori(mask,(1<<(n-1))){
        ll cur = __builtin_popcount(mask);
        vi cnt(m);
        int st = 0;
        vvi foo;
        fori(i,n){
            if(i==n-1 or ((mask&(1<<i))!=0)){
                rep(ii,st,i){
                    fori(j,m){
                        cnt[j] += (a[ii][j]=='1');
                    }
                } 
                bool ok = (cnt[0] <= k);
                rep(j,1,m-1){
                    ok &= (cnt[j] <= k);
                    cnt[j] += cnt[j-1];
                }
                foo.pb(cnt);
                if(!ok) {
                    cur = INF;
                    break;
                }
                fori(j,m){
                    cnt[j] = 0;
                }
                st = i+1;
            }
        }
        if(cur == INF) continue;

        int _n = sz(foo);
        vi ptr(_n);
        int ind = 0;
        while(ind < m){
            cur++;
            int _ind = m;
            fori(j,sz(foo)){
                int my = upper_bound(all(foo[j]),(ind ? foo[j][ind-1] + k : k)) - foo[j].begin();
                _ind = min(_ind,my);
            }
            ind = _ind;
        }
        ans = min(ans,cur-1);
        // trace(mask,cur);
    }

    cout << ans << endl;

    time_taken();
    return 0;
}

Measured memory_bytes: 384