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

#define NDEBUG
#include <cassert>


typedef long long ll;
typedef long double Double;
typedef unsigned long long ull;
typedef pair<int,int> ii;
typedef pair<ll,ll> llll;
typedef pair<double,double> dd;

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<llll> vllll;
typedef vector<bool> vb;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<long double> vD;

#define sz(a)  int((a).size())
#define pb  push_back
#define eb  emplace_back
#define FOR(var,from,to) for(int var=(from);var<=(to);++var)
#define rep(var,n)  for(int var=0;var<(n);++var)
#define rep1(var,n)  for(int var=1;var<=(n);++var)
#define repC2(vari,varj,n)  for(int vari=0;vari<(n)-1;++vari)for(int varj=vari+1;varj<(n);++varj)
#define repC3(vari,varj,vark,n)  for(int vari=0;vari<(n)-2;++vari)for(int varj=vari+1;varj<(n)-1;++varj)for(int vark=varj+1;vark<(n);++vark)
#define ALL(c)  (c).begin(),(c).end()
#define RALL(c)  (c).rbegin(),(c).rend()
#define tr(i,c)  for(auto i=(c).begin(); i!=(c).end(); ++i)
#define found(s,e)  ((s).find(e)!=(s).end())
#define mset(arr,val)  memset(arr,val,sizeof(arr))
#define mid(x,y) ((x)+((y)-(x))/2)
#define IN(x,a,b) ((a)<=(x)&&(x)<=(b))
#define cons make_pair
#define clamp(v,lo,hi) min(max(v,lo),hi)
#define ABS(x) max((x),-(x))

template<typename T1, typename T2> inline void amin(T1 & a, T2 const & b) { if (a>b) a=b; }
template<typename T1, typename T2> inline void amax(T1 & a, T2 const & b) { if (a<b) a=b; }
template<typename X, typename T> auto vectors(X x, T a) { return vector<T>(x, a); }
template<typename X, typename Y, typename Z, typename... Zs> auto vectors(X x, Y y, Z z, Zs... zs) { auto cont = vectors(y, z, zs...); return vector<decltype(cont)>(x, cont); }

inline ll square(ll x) { return x * x; }
inline ll gcd(ll a, ll b) { while(a) swap(a, b%=a); return b; }
inline ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }
template <typename T>
inline T mod(T a, T b) { return ((a % b) + b) % b; }

template <typename T>
int find_left(vector<T>& v, T elem) {
    return (int)(upper_bound(v.begin(), v.end(), elem) - v.begin()) - 1;
}
template <typename T>
int find_right(vector<T>& v, T elem) {
    return (int)(lower_bound(v.begin(), v.end(), elem) - v.begin());
}

const ll MOD=1000000007LL;

inline ll ADD(ll x, ll y) { return (x+y) % MOD; }
inline ll SUB(ll x, ll y) { return (x-y+MOD) % MOD; }
inline ll MUL(ll x, ll y) { return x*y % MOD; }
inline ll POW(ll x, ll e) { ll v=1; for(; e; x=MUL(x,x), e>>=1) if (e&1) v = MUL(v,x); return v; }
inline ll INV(ll y) { /*assert(y%MOD!=0);*/ return POW(y, MOD-2); }
inline ll DIV(ll x, ll y) { return MUL(x, INV(y)); }

#define INTSPACE 12
char _buf[INTSPACE*1000000 + 3];

int loadint() {
    if (fgets(_buf, INTSPACE+3, stdin)==NULL) return 0;
    return atoi(_buf);
}

int loadvec(vector<int>& v, int N=-1) {
    if (N == 0) {
        v.clear();
        return 0;
    }
    if (N == -1) {
        N = loadint();
        if (N==0) return 0;
    }
    int bufsize = INTSPACE*N + 3;
    if (fgets(_buf, bufsize, stdin)==NULL) return 0;
    v.resize(N);

    int i=0;
    bool last = false;
    for (char *p=&_buf[0]; ;) {
        char *q = p;
        while (*q > ' ') ++q;
        if (*q == 0x0D || *q == 0x0A) last = true;
        *q = 0;
        v[i++] = atoi(p);
        if (last || i == N) break;
        p = q+1;
    }
    return i;
}
void read_cr() {
    fgets(_buf, 256, stdin);
}

void horizontal(vector<int>& v) {
    int L = v.size();
    for (int i=0; i<L; ++i) {
        printf("%d%c", v[i], (i==L-1)?'\n':' ');
    }
}
void horizontall(vector<long long>& v) {
    int L = v.size();
    for (int i=0; i<L; ++i) {
        printf("%lld%c", v[i], (i==L-1)?'\n':' ');
    }
}

template <typename T>
vector<T> imos1d(vector<T>& a) {
    int L = a.size();
    vector<T> res(L+1);
    res[0] = 0;
    for (int i=0; i<L; ++i) res[i+1] = res[i] + a[i];
    return std::move(res);
}

template <typename T>
vector<vector<T>> imos2d(vector<vector<T>>& a) {
    int R = a.size();
    if (R == 0) return vector<vector<T>>();
    int C = a[0].size();
    vector<vector<T>> res(R+1);
    res[0].assign(C+1, 0);
    for (int r=0; r<R; ++r) {
        res[1+r] = imos1d(a[r]);
    }
    for (int c=0; c<=C; ++c) {
        for (int r=0; r<R; ++r) {
            res[r+1][c] += res[r][c];
        }
    }
    return std::move(res);
}

template <typename T1, typename T2>
vector<T2> accum(vector<T1>& a, T2 init) {
    int L = a.size();
    vector<T2> acc(L + 1);
    acc[0] = init;
    for (int i=0; i<L; ++i) acc[i+1] = acc[i] + a[i];
    return move(acc);
}

template <typename T>
T accumed(vector<T>& acc, int from, int to) {
    int M = acc.size() - 1;
    return acc[min(M, to)] - acc[max(0, from)];
}
int sub(int W,int K,vs& s){
    vvi a(10, vi(W, 0));
    rep(r,10) rep(c,W){
        a[r][c] = s[r][c] - '0';
    }

    vi tm(W,0);
    rep(c,W){
        rep(i,10){
            tm[c] |= (a[i][c] << i);
        }
    }

    vvi aru(1024, vi(W));
    vvi aruc(1024);
    rep(pat,1024){
        rep(c,W){
            int pc = __builtin_popcount(tm[c] & pat);
            aru[pat][c] = pc;
        }
        aruc[pat] = accum(aru[pat], 0);
    }

    int best = INT_MAX;

    for(int cut=0; cut<512; ++cut){
        int cutcost = __builtin_popcount(cut);
        vi t; t.pb(0);
        for(int b=0,m=1; b<9; ++b,m<<=1){
            if (cut&m) t.pb(1+b);
        }
        t.pb(10); int T=t.size()-1;
        vi h(T);
        rep(i,T) h[i] = t[i+1]-t[i];
        vi pt(T);
        rep(i,T) pt[i] = ((1 << h[i])-1) << t[i];
        int lo=0;
        while (lo < W){
            int himin = INT_MAX;
            rep(i,T){
                int pat = pt[i];
                auto hit = upper_bound(ALL(aruc[pat]), aruc[pat][lo]+K)-1;
                if (hit != aruc[pat].end()) {
                    if (*hit > aruc[pat][lo]+K) --hit;
                }
                int hi = hit - aruc[pat].begin();
                if (accumed(aruc[pat],lo,hi) > K) goto impossible;
                amin(himin, hi);
            }
            if (himin == lo) goto impossible;
            lo = himin; ++cutcost;
        }
        amin(best, cutcost);
    impossible:
        ;
    }
    return best-1;
}

int solve(int H,int W,int K,vs& s) {
    string black(W,'0');
    if (H < 10) s.resize(10,black);
    return sub(W,K,s);
}

int main() {
    int H,W,K; cin >> H >> W >> K;
    vs s(H);
    rep(i,H) cin>>s[i];
    cout << solve(H,W,K,s) << endl;
    return 0;
}


Measured memory_bytes: 8320