Problem:
Score : 500 points

Problem Statement

We have a chocolate bar partitioned into H horizontal rows and W vertical columns of squares.

The square (i, j) at the i-th row from the top and the j-th column from the left is dark if S_{i,j} is 0, and white if S_{i,j} is 1.

We will cut the bar some number of times to divide it into some number of blocks. In each cut, we cut the whole bar by a line running along some boundaries of squares from end to end of the bar.

How many times do we need to cut the bar so that every block after the cuts has K or less white squares?

Constraints

1 \leq H \leq 10

1 \leq W \leq 1000

1 \leq K \leq H \times W

S_{i,j} is 0 or 1.

Input

Input is given from Standard Input in the following format:

H W K
S_{1,1}S_{1,2}...S_{1,W}
:
S_{H,1}S_{H,2}...S_{H,W}

Output

Print the number of minimum times the bar needs to be cut so that every block after the cuts has K or less white squares.

Sample Input 1

3 5 4
11100
10001
00111

Sample Output 1

2

For example, cutting between the 1-st and 2-nd rows and between the 3-rd and 4-th columns - as shown in the figure to the left - works.

Note that we cannot cut the bar in the ways shown in the two figures to the right.

Sample Input 2

3 5 8
11100
10001
00111

Sample Output 2

0

No cut is needed.

Sample Input 3

4 10 4
1110010010
1000101110
0011101001
1101000111

Sample Output 3

3

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
#include <regex>
#define FOR(i, s, e) for (ll i = ll(s); i < ll(e); ++i)
#define REP(i, e) FOR(i, 0, e)
#define INF (INT_MAX / 2)
#define LINF (LLONG_MAX / 2)
#define EPS (1.0e-8)
#define mkpr make_pair
#define EPR(msg) cerr << msg << endl;
#define AST(exp, msg) if(!exp){EPR(msg)} assert(exp);
#define TAST(exp, msg) if(!exp){EPR(msg)} while(!exp){}
const int MGN = 10;
const int ARY_SZ_MAX = (int)1e7;
using namespace std;
using ll = long long; using ull = unsigned long long;
using vi = vector<int>; using vvi = vector<vi>;
using vc = vector<char>; using vvc = vector<vc>;
using vb = vector<bool>; using vvb = vector<vb>;
using vl = vector<ll>; using vvl = vector<vl>;
using vd = vector<double>; using vs = vector<string>;
using pii = pair<int, int>; using pll = pair<ll, ll>; using psl = pair<string, ll>;


int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  const ll HMAX = 10, WMAX = 1000;
  ll H, W, K; cin>>H>>W>>K;
  vs S(H); REP(i,H) cin>>S[i];

  // H 行の行間の H-1 ラインを切るか切らないかのパターン
  const ll HPTN = 1LL<<(H-1);
  ll ans = LINF;

  REP(ptn, HPTN) {
    vl hgp(1, 0);  // 水平方向にわけたグループに含まれる 1 の数
    vl i2g(H, 0);  // i 行目は g グループに属する
    
    FOR(i, 1, H) {
      if ((1LL<<i) & ptn) { // i 行目の上を切るなら
        hgp.push_back(0);
      }
      i2g[i] = hgp.size() - 1;
    }
    const ll GSZ = hgp.size();
    AST(i2g[0] == 0, "最初の行は最初のグループに属する");    
    AST(i2g[H-1] == GSZ-1, "最後の行は最後のグループに属する");
    
    ll hcut = GSZ-1;

    // j 列目を各グループに加算してみる
    ll vcut = 0;
    bool ok = true;  // この水平グループで実現可能か
    bool reset = false;
    REP(j,W) {
      REP(i,H) {
        if (S[i][j] == '1') {
          if (hgp[i2g[i]] >= K) {
            if (j == 0 || reset) {
              ok = false;
              break;
            }
            j--;
            vcut++;
            hgp = vl(GSZ, 0);
            reset = true;
            break;
          }
          hgp[i2g[i]] += 1;
        }
      }
      reset = false;
      if (!ok) vcut = LINF;
    }

    ans = min(ans, hcut+vcut);
  }

  cout << ans << endl;


  return 0;
}