#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using lint128 = __int128_t;
const lint mod = 998244353;
#define all(x) (x).begin(), (x).end()
#define bitcount(n) __builtin_popcountl((lint)(n))
#define fcout cout << fixed << setprecision(15)
#define highest(x) (63 - __builtin_clzl(x))
template<class T> inline void YES(T condition){ if(condition) cout << "YES" << endl; else cout << "NO" << endl; }
template<class T> inline void Yes(T condition){ if(condition) cout << "Yes" << endl; else cout << "No" << endl; }
template<class T> inline void assert_NO(T condition){ if(!condition){ cout << "NO" << endl; exit(0); } }
template<class T> inline void assert_No(T condition){ if(!condition){ cout << "No" << endl; exit(0); } }
template<class T> inline void assert_minus_1(T condition){ if(!condition){ cout << -1 << endl; exit(0); } }
lint power(lint base, lint exponent, lint module){ if(exponent % 2){ return power(base, exponent - 1, module) * base % module; }else if(exponent){ lint root_ans = power(base, exponent / 2, module); return root_ans * root_ans % module; }else{ return 1; }}
struct position{ int y, x; }; position mv[4] = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}}; // double euclidean(position first, position second){ return sqrt((second.x - first.x) * (second.x - first.x) + (second.y - first.y) * (second.y - first.y)); }
template<class T, class U> string to_string(pair<T, U> x){ return to_string(x.first) + "," + to_string(x.second); } string to_string(string x){ return x; }
template<class itr> void array_output(itr start, itr goal){ string ans; for(auto i = start; i != goal; i++) ans += to_string(*i) + " "; if(!ans.empty()) ans.pop_back(); cout << ans << endl; }
template<class itr> void cins(itr first, itr last){ for(auto i = first; i != last; i++){ cin >> (*i); } }
template<class T> T gcd_calc(T a, T b){ if(b){ return gcd_calc(b, a % b); }else{ return a; }}
template<class T> T gcd(T a, T b){ if(a < b) swap(a, b); return gcd_calc(a, b); }
template<class T> T lcm(T a, T b){ return a / gcd(a, b) * b; }
struct combination{ vector<lint> fact, inv; combination(int sz) : fact(sz + 1), inv(sz + 1){ fact[0] = 1; for(int i = 1; i <= sz; i++){ fact[i] = fact[i - 1] * i % mod; } inv[sz] = power(fact[sz], mod - 2, mod); for(int i = sz - 1; i >= 0; i--){ inv[i] = inv[i + 1] * (i + 1) % mod; } } lint C(int p, int q) const{ if(q < 0 || p < q) return 0; return (fact[p] * inv[q] % mod * inv[p - q] % mod); } };
template<class itr> bool next_sequence(itr first, itr last, int max_bound){ itr now = last; while(now != first){ now--; (*now)++; if((*now) == max_bound){ (*now) = 0; }else{ return true; } } return false; }
template<class T> bool chmax(T &a, const T &b){ if(a < b){ a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b){ if(b < a){ a = b; return 1; } return 0; }
inline int at(lint x, int k){ return (x >> k) & 1; }
random_device rnd;
#define rep(i, n) for(int i = 0; i < n; i++)

int main(){
    int H, W, K;
    cin >> H >> W >> K;
    string S_str[H];
    cins(S_str, S_str + H);
    vector<int> S[H];
    rep(i, H){
        rep(j, W){
            S[i].push_back(S_str[i][j] - '0');
        }
    }
    int ans = 1e9;
    rep(i, (1 << (H - 1))){
        vector<vector<int>> S2;
        S2.push_back(S[0]);
        rep(j, H - 1){
            if(at(i, j)){
                S2.push_back(S[j + 1]);
            }else{
                rep(k, W){
                    S2.back()[k] += S[j + 1][k];
                }
            }
        }
        vector<int> sum(S2.size(), 0);
        int cutting = bitcount(i);
        rep(j, W){
            bool is_cut = false;
            rep(k, S2.size()){
                if(S2[k][j] > K){
                    goto pass;
                }
                if(sum[k] + S2[k][j] > K){
                    is_cut = true;
                }
            }
            if(is_cut){
                cutting++;
                rep(k, S2.size()){
                    sum[k] = S2[k][j];
                }
            }else{
                rep(k, S2.size()){
                    sum[k] += S2[k][j];
                }
            }
        }
        ans = min(ans, cutting);
    pass:;
    }
    cout << ans << endl;
}


Measured memory_bytes: 384