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: Runtime Error)

require "pp"

class Main
  def run()
    @n, @m = gets.split(" ").map(&:to_i)
    @graph = {}
    @m.times do |i|
      x, y = gets.split(" ").map(&:to_i)

      @graph[x] ||= []
      @graph[y] ||= []
      @graph[x] << y
      @graph[y] << x
    end

    (1..@n).each do |i|
      @graph[i] ||= []
    end

    @res = {}
    (1..@n).each do |i|
      dfs(i, i)
    end

    puts @res.values.uniq.count
  end

  def dfs(i, mark)
    unless @res[i].nil?
      return
    end

    @res[i] = mark
    @graph[i].each do |x|
      dfs(x, mark)
    end
  end
end

main = Main.new()
main.run()