Problem:
Score : 500 points

Problem Statement

There are N cards placed face down in a row. On each card, an integer 1 or 2 is written.

Let A_i be the integer written on the i-th card.

Your objective is to guess A_1, A_2, ..., A_N correctly.

You know the following facts:

For each i = 1, 2, ..., M, the value A_{X_i} + A_{Y_i} + Z_i is an even number.

You are a magician and can use the following magic any number of times:

Magic: Choose one card and know the integer A_i written on it. The cost of using this magic is 1.

What is the minimum cost required to determine all of A_1, A_2, ..., A_N?

It is guaranteed that there is no contradiction in given input.

Constraints

All values in input are integers.

2 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq X_i < Y_i \leq N

1 \leq Z_i \leq 100

The pairs (X_i, Y_i) are distinct.

There is no contradiction in input. (That is, there exist integers A_1, A_2, ..., A_N that satisfy the conditions.)

Input

Input is given from Standard Input in the following format:

N M
X_1 Y_1 Z_1
X_2 Y_2 Z_2
\vdots
X_M Y_M Z_M

Output

Print the minimum total cost required to determine all of A_1, A_2, ..., A_N.

Sample Input 1

3 1
1 2 1

Sample Output 1

2

You can determine all of A_1, A_2, A_3 by using the magic for the first and third cards.

Sample Input 2

6 5
1 2 1
2 3 2
1 3 3
4 5 4
5 6 5

Sample Output 2

2

Sample Input 3

100000 1
1 100000 100

Sample Output 3

99999

Solution in Ruby (2.3.3) (judge verdict: Time Limit Exceeded)

n, m = gets.rstrip.split.map(&:to_i)
xyzs = m.times.map{ gets.rstrip.split.map(&:to_i) }
xys = []; xyzs.each{|xyz| xys << [xyz[0], xyz[1]]}

deleted = []
ans = 0


#
# xys から 左 or 右 に x を含む行を削除.
#   左 に x を含む場合は再帰的に 右 を含む行を削除
#   右 に x を含む場合は再帰的に 左 を含む行を削除
def rm_relevant(xys, deleted, x)
  return xys, deleted if deleted.include? x
  deleted << x

  to_del = []

  xys.reject! do | xy |
    if xy[0] == x
      to_del << xy[1] unless deleted.include? xy[1]
    end
    if xy[1] == x
      to_del << xy[0] unless deleted.include? xy[0]
    end
    xy[0] == x or xy[1] == x # x を含む行を削除
  end

  to_del.each do | x |
    xys, deleted = rm_relevant(xys, deleted, x)
  end
  return xys, deleted
end

while xys.size > 0
  xy = xys.shift
  xys, deleted = rm_relevant(xys, deleted, xy[0])
  xys, deleted = rm_relevant(xys, deleted, xy[1])
  ans += 1
end

p ans + n - deleted.size