// Problem : E - Dividing Chocolate
// Contest : AtCoder Beginner Contest 159
// URL : https://atcoder.jp/contests/abc159/tasks/abc159_e
// Memory Limit : 1024 MB
// Time Limit : 2000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

//Zory-2020
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
// typedef __int128 ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define FR first
#define SE second
#define MP make_pair
#define PB push_back
#define vc vector
#define db double
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define bin(x) (1ll<<(x))
#define fo(i,l,r) for(int i=(l),I=(r);i<=I;i++)
#define fd(i,r,l) for(int i=(r),I=(l);i>=I;i--)
#define mem(x,val) memset(x,val,sizeof x)
#define Swap(a,b,n) for(int I=0;I<=n;I++) swap(a[I],b[I])
#define PC __builtin_popcountll
#ifdef DEBUG
	#define debug(A,args...) fprintf(stderr,A,##args)
#else
	#define debug(A,args...) printf("")
#endif
#define deb debug("line %d\n",__LINE__)
namespace mine
{
	ll qread()
	{
		ll ans=0,f=1;char c=getchar();
		while(c<'0' or c>'9') {if(c=='-')f=-1;c=getchar();}
		while('0'<=c and c<='9') ans=ans*10+c-'0',c=getchar();
		return ans*f;
	}
	void write(ll num){if(num<0) putchar('-'),num=-num;if(num>=10) write(num/10);putchar('0'+num%10);}
	void write1(ll num){write(num);putchar(' ');}
	void write2(ll num){write(num);putchar('\n');}
	template<typename T>inline bool chmax(T&a,const T&b){return a<b?a=b,1:0;}
	template<typename T>inline bool chmin(T&a,const T&b){return a>b?a=b,1:0;}
	ll gcd(ll x,ll y){return y?gcd(y,x%y):x;}
	bool IN(ll x,ll l,ll r){return l<=x and x<=r;}
	void GG(){puts("-1");exit(0);}

	const db eps=1e-8;
	const int INF=0x3f3f3f3f;
	const int MOD=1e9+7;
	int mm(const int x){return x>=MOD?x-MOD:x;}
	template<typename T> void add(T &x,const int &y){x=(x+y>=MOD?x+y-MOD:x+y);}
	ll qpower(ll x,ll e,int mod=MOD){ll ans=1;while(e){if(e&1)ans=ans*x%mod;x=x*x%mod;e>>=1;}return ans;}
	ll invm(ll x){return qpower(x,MOD-2);}
	const int MM=5e6+10;
	ll fac[MM],facinv[MM],Inv[MM];ll Comb(int n,int m){return n<0 or n<m?0:fac[n]*facinv[m]%MOD*facinv[n-m]%MOD;}
	void PRE()
	{
		fac[0]=1;fo(i,1,MM-1) fac[i]=fac[i-1]*i%MOD;
		facinv[MM-1]=invm(fac[MM-1]);fd(i,MM-1,1) facinv[i-1]=facinv[i]*i%MOD;
		Inv[1]=1;fo(i,2,MM-1) Inv[i]=(MOD-MOD/i)*Inv[MOD%i]%MOD;
	}

	const int N=1e5+10;
	//------------------FIXED------------------
	char mp[20][N];int cnt[20],go[20];
	void main()
	{
		int n=qread(),m=qread(),K=qread();
		fo(i,0,n-1) scanf("%s",mp[i]+1);
		int ans=INF;
		fo(s,0,bin(n-1)-1)
		{
			int lst=0;fo(i,0,n-1) {go[i]=lst;if(s&bin(i))lst=i+1;} mem(cnt,0);
			int sum=0,gg=0;fo(j,1,m){
				fo(i,0,n-1)if(mp[i][j]=='1')cnt[go[i]]++;
				int mx=0;fo(i,0,n-1) chmax(mx,cnt[i]);
				if(mx>K){ mem(cnt,0);sum++;fo(i,0,n-1)if(mp[i][j]=='1')cnt[go[i]]++; }
				mx=0;fo(i,0,n-1) chmax(mx,cnt[i]);if(mx>K){gg=1;}
			}if(!gg) chmin(ans,sum+PC(s));
			if(sum+PC(s)==1)
				debug("s=%d\n",s);
		}write(ans);
	}
};//变量重名！
signed main()
{
	#ifdef DEBUG
	//freopen("a.in","r",stdin);
	// freopen("z.txt","r",stdin);
	//freopen("a.out","w",stdout);
	#endif
	srand(time(0));
	mine::main();
	//debug("\n------------------------------------------\nTime: %.2lf s\n",1.0*clock()/CLOCKS_PER_SEC);
}

Measured memory_bytes: 256