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 Ruby (2.3.3) (judge verdict: Accepted)

INF = 10 ** 5
h, w, k = gets.split.map(&:to_i)
chocolate = []
h.times { chocolate << gets.chomp.split("").map(&:to_i) }

# 0 の時は i 行目の下を横方向に分割しない、1 なら分割する
divisions = []
queue = [[]]
until queue.empty?
  tmp = queue.shift
  if tmp.size == h - 1
    divisions << tmp
  else
    queue << tmp + [0]
    queue << tmp + [1]
  end
end

# 横方向に分割後のチョコレート全通りを divided に入れる
# 21212
#
# 21101
# 00111
#
# 11100
# 10112
#
# 11100
# 10001
# 00111
divided = []
divisions.each do |division|
  tmp = []
  current_white = chocolate.first.dup
  division.each_with_index do |d, i|
    next_row = chocolate[i + 1].dup
    if d == 0
      (0...w).each { |c| current_white[c] += next_row[c] }
    else
      tmp << current_white
      current_white = next_row
    end
  end
  tmp << current_white
  divided << tmp
end
# divided.each { |d| p d }

counts = []
divided.each do |d|
  vertical_count = 0
  tmp_white = Array.new(d.size, 0)
  # どれか 1 行でもホワイトチョコレートが k を超えてしまったら分割
  (0...w).each do |i|
    add_white = d.map { |row| row[i] }
    add_white.each_with_index do |c, i|
      if c > k
        vertical_count = INF
        break
      end
      tmp_white[i] += c
    end
    if tmp_white.any? { |c| c > k }
      vertical_count += 1
      tmp_white = add_white
    end
  end
  counts << d.size - 1 + vertical_count
end
puts counts.min