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: Wrong Answer)

class UnionFindTree
  class Node
    attr_accessor :parent, :rank

    def initialize(n)
      @parent = n
      @rank = 0
    end
  end

  attr_reader :nodes
  private :nodes

  def initialize(n)
    @nodes = Array.new(n) { |i| Node.new(i) }
  end

  def find(x)
    if nodes[x].parent == x
      x
    else
      # shortcut
      nodes[x].parent = find(nodes[x].parent)
    end
  end

  alias root find

  # whether in the same group
  def same?(a, b)
    find(a) == find(b)
  end

  def unite(a, b)
    # parents
    a = find(a)
    b = find(b)
    return if a == b

    # shortcut
    a, b = b, a if nodes[a].rank < nodes[b].rank
    nodes[a].rank += 1 if nodes[a].rank == nodes[b].rank

    nodes[b].parent = a
  end

  alias merge unite

  def roots
    nodes.map(&:parent)
  end
end

n, m = gets.split.map(&:to_i)

uft = UnionFindTree.new(n)

m.times do
  x, y, _ = gets.split.map(&:to_i)
  uft.merge(x - 1, y - 1)
end

require 'set'
p uft.roots.to_set.size