// Marcin Knapik
#include<bits/stdc++.h>
// #pragma GCC optimize("O3")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
using namespace std;

// #include <ext/pb_ds/assoc_container.hpp> // order_of_key
// #include <ext/pb_ds/tree_policy.hpp> // find by order
// using namespace __gnu_pbds; 
// #define ordered_set tree< int , null_type,less< int >, rb_tree_tag,tree_order_statistics_node_update>  

// const ll MAX_LL = 0xFFFFFFFFFFFFFFFF;
// mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
// #define losuj(a, b) uniform_int_distribution<ull>(a, b)(rng)

typedef long double             ld;
typedef long long               ll;
typedef unsigned long long      ull;
typedef pair<ll, ll>            pll;
typedef pair<int, int>          ii;
typedef vector<int>             vi;
typedef vector<ii>              vii;
typedef vector<vi>              vvi;
typedef vector<vector<ii>>      vvii;
typedef vector< ll >            vll;
typedef vector< pll >           vpll;

#define boost                   ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define sz(a)                   (int)(a).size()
#define pb                      push_back
#define all(c)                  (c).begin(), (c).end()
#define rall(c)                 (c).rbegin(), (c).rend()
#define FOR(i, a)               for (int i = 0; i < (a); i++)
#define f                       first
#define s                       second

template <class T> inline bool setmin(T &a, T b){if (a > b)return a = b, 1;return 0;}
template <class T> inline bool setmax(T &a, T b){if (a < b)return a = b, 1;return 0;}

template<class T> inline T fast(T a,T b,T mod) {ll res = 1; while(b){if(b&1) res = (res*a)%mod;a = (a*a)%mod;b >>= 1;}return res;}
template<class T> inline T russian(T a, T b, T mod) {ll res = 0; while(b){if(b&1) res = (res + a)%mod; a = (a+a)%mod; b>>=1;}return res;}
template<class T> istream &operator>>(istream &os, vector<T> &container){for (auto &u : container)os >> u;return os;}
template<class T> ostream &operator<<(ostream &os, const vector<T> &container){for (auto &u : container)os << u << " ";return os;}
template<class T> inline T gcd(T a, T b) { while (b)swap(a %= b, b); return a; }

const ll INF = 1e9 + 7;
const ll mod = 1186782211;
// const ll BIG_INF = 1000000000000000000;
const ll BIG_INF = 15000000000000;
const ll N = 1e6+7;
const ll T = 1<<20;
const ll Hope = 1000000123;

ll n, m, k, q;	

ll ile[N];
char tab[15][N];

int ans = INF;

void solve(int mask){
	int ret = __builtin_popcount(mask);
	vi paski(n+1, 0);
	vi maping(n, 0);

	int id = 0;
	for(int i = 0; i < n; i++){
		maping[i] = id;
		if(mask & (1<<i))
			id++;
	}
	int last = 0;
	for(int j = 0; j < m; j++){
		for(int i = 0; i < n; i++)
			if(tab[i][j] == '1')
				paski[maping[i]]++;
		for(int i = 0; i < n; i++)
			if(paski[i] > k){
				ret ++;
				if(last == j)
					return;
				last = j;
				j--;
				for(int l = 0; l < n; l++)
					paski[l] = 0;
				break;
			}
	}
	ans = min(ans, ret);
}

int main(){
	boost;

	cin >> n >> m >> k;

	for(int i = 0; i < n; i++)
		for(int j = 0; j < m; j++)
			cin >> tab[i][j];

	for(int i = 0; i < (1<<(n-1)); i++)
		solve(i);

	cout << ans << '\n';
}

Measured memory_bytes: 8448