#include<bits/stdc++.h>
 
using namespace std;

template <class T> ostream& operator << (ostream &os, const vector<T> &v) { for (T i : v) os << i << ' '; return os; }
template <class T> ostream& operator << (ostream &os, const set<T> &v) { for (T i : v) os << i << ' '; return os; }
template <class T, class S> ostream& operator << (ostream &os, const pair<T, S> &v) { os << v.first << ' ' << v.second; return os; }
template <class T, class S> ostream& operator << (ostream &os, const map<T, S> &v) { for (auto i : v) os << '(' << i.first << "=>" << i.second << ')' << ' '; return os; }
template <class T, class S> ostream& operator << (ostream &os, const unordered_map<T, S> &v) { for (auto i : v) os << '(' << i.first << "=>" << i.second << ')' << ' '; return os; }
 
#ifndef ONLINE_JUDGE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
    template <class Arg1> void __f(const char* name, Arg1&& arg1) { cerr << name << " : " << arg1 << endl; }
    template <class Arg1, class... Args>
    void __f(const char* names, Arg1&& arg1, Args&&... args) {
        const char* sep = strchr(names + 1, ',');
        cerr.write(names, sep - names) << " : " << arg1 << "  ";
        __f(sep + 1, args...);
    }
#else
#define trace(...) 0
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx2,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define _CRT_SECURE_NO_WARNINGS
#endif

#define fast_cin() ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define MAX 1000000
#define ll long long
#define db double
#define str string
#define pb push_back
#define For(i,s,e) for (ll i=(s); i<(e); i++)
#define Forrev(i,s,e) for (ll i=(s); i>=(e); i--)
#define all(v) v.begin(),v.end()

#define vll vector<ll>
#define vs vector<string>
#define mapll map<ll,ll>
#define pll pair<ll,ll>
#define initialise(a, x) memset(a, x, sizeof(a))
#define maxheap priority_queue<ll>
#define minheap priority_queue<ll,vector<ll> ,greater<ll>>

#define ff first
#define ss second
#define endl "\n"
#define mp make_pair
const ll mod=1e9 + 7;

ll takemod(ll a) {
    return ((a%mod)+mod)%mod;
}

ll gcd(ll a, ll b) { 
    if (b == 0) 
        return a; 
    return gcd(b, a % b);        
}

ll fast_exp(ll base, ll expo) {
    ll res=1;
    while(expo>0) {
        if(expo&1) res=(res*base)%mod;
        base=(base*base)%mod;
        expo>>=1;}
    return res;
}

ll modinv(ll a) {
    return takemod(fast_exp(takemod(a), mod-2));
}

ll arr[11][1001];
ll n,m,k,ans;

void dpfunc(ll index, ll val)
{
	if(index==n-1)
	{
		ll temp=0;
		vector<pll> v1;
		ll prev=0;
		For(i,0,n)
		{
			if((val&(1LL<<i))!=0)
			{
				temp++;
				v1.pb(mp(prev,i));
				prev=i+1;
			}
		}

		//cout<<val<<" "<<temp<<endl;
		v1.pb(mp(prev,n-1));

        ll cnts[v1.size()];
        memset(cnts,0,sizeof(cnts));

        For(j,0,m)
        {
            For(i,0,v1.size())
            {
                For(l,v1[i].ff,v1[i].ss+1)
                    cnts[i]+=arr[l][j];
            }

            ll tempflag=0;
            For(i,0,v1.size())
            {
                if(cnts[i]>k)
                    tempflag=1;
            }
            if(tempflag==1)
            {
                memset(cnts,0,sizeof(cnts));
                For(i,0,v1.size())
	            {
	                For(l,v1[i].ff,v1[i].ss+1)
	                    cnts[i]+=arr[l][j];
	            }
	            tempflag=0;
	            For(i,0,v1.size())
	            {
	                if(cnts[i]>k)
	                    tempflag=1;
	            }
	            if(tempflag==1)
	            {
	            	temp=10000000000;
	            	break;
	            }

                temp++;
            }
        }
        ans=min(ans,temp);
	}
	else
	{
		dpfunc(index+1,val);
		dpfunc(index+1,(1LL<<index)+val);
	}
}

void solve()
{
	cin>>n>>m>>k;
	For(i,0,n)
	{
		string s;
		cin>>s;
		For(j,0,m)
			arr[i][j]=s[j]-'0';
	}

	ans=100000000000;
	dpfunc(0,0);
	cout<<ans<<endl;
}

signed main() 
{
    fast_cin();
    // #ifndef ONLINE_JUDGE
    // freopen("C:/IO/in.txt", "r", stdin);
    // freopen("C:/IO/out.txt", "w", stdout);
    // #endif
    
    int t=1;
    //cin>>t;
    while(t--)
    {
    	solve();
    }
    
    
    return 0;    
}

Measured memory_bytes: 384