/*
 * zyrch - Rupanshu Yadav
 */
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <fstream>
#include <queue>
#include <deque>
#include <bitset>
#include <iterator>
#include <list>
#include <stack>
#include <map>
#include <set>
#include <functional>
#include <utility>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <cassert>
#include <sstream>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef double db;
typedef string str;

typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;

typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<ld> vd;
typedef vector<str> vs;
typedef vector<pi> vpi;
typedef vector<pl> vpl;

#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL) 

#define forn(i,a,b) for (int i = (a); i < ll(b); ++i)
#define fo(i,a) forn(i,0,ll(a))
#define rforn(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define ro(i,a) rforn(i,0,a)
#define trav(a,x) for (auto& a: x)

#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define rsz resize
#define ins insert

#define mp make_pair
#define pb push_back
#define eb emplace_back
#define f first
#define s second

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif

const ll INF = 1e18;

ll mod = 1000000007;
inline ll fast_expo(ll base,ll power,ll modulo=mod){
    base%=modulo;
    if (base<0) base+=modulo;
    ll x=base,cnt=power,ans=1;
    while(cnt){
        if (cnt&1) ans=(ans*x)%modulo;
        x=(x*x)%modulo;
        cnt>>=1;
    }
    return ans;
}

ll takemod(ll a, ll mo){
	a %= mo;
	if(a < 0) a+=mo;
	return a;
}

// if mod is prime
ll modinv(ll a, ll mo){
	return takemod(fast_expo(takemod(a,mo), mo-2, mo), mo);
}

//=========================CODE STARTS HERE=============================//

int main() {
	
	ll h, w, k;
	cin >> h >> w >> k;

	vector<vector<int>> matrix(h, vector<int> (w));
	str s;
	fo(i, h) {
		cin >> s;
		//~ debug(scatc);
		fo(j, w) {
			matrix[i][j] = s[j] - '0';
			//~ debug(matrix[i][j], s[i] - '0', s[i]);
		}
	}
	ll ans = INF;
	//~ debug(matrix);
	int re = -1;
	for (int i = 0; i < (1 << h); ++i) {
		
		vl count(__builtin_popcount(i) + 1, 0);
		ll loc = 0;
		ll ti = 0;
		fo(j, w) {
			x:
			ti = 0;
			count[0] += matrix[0][j];
			forn(o, 1, h) {
				if (i & (1 << (o - 1))) {
					ti++;
				}
				count[ti] += matrix[o][j];
				//~ cout << matrix[0]
			}
			//~ debug(j, count);
			trav(o, count) {
				if (o > k) {
					loc += 1;
					count.resize(__builtin_popcount(i) + 1);
					//~ debug(count);
					count.assign(count.size(), 0);
					//~ debug(count);
					//~ fo(t, count.size()) count[t] = 0;
					
					if (re == j) {
						break;
					}
					re = j;
					goto x;
					//~ break;
					//~ --j;
				}
			}
		}
		//~ debug(i);
		//~ debug(i, loc + __builtin_popcount(i));
		ans = min(ans, loc + __builtin_popcount(i));
	}
	cout << ans << endl;
	
	return 0; 
}


Measured memory_bytes: 256