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 'set'
require 'tsort'

n, m = gets.chomp!.split(" ").map!(&:to_i)
xyz = Array.new(m) {|index| Array.new(0, m) }

xyzs = {}
xyz.each.with_index(1) do |_, i|
    x_i, y_i, z_i = gets.chomp!.split(" ").map!(&:to_i)
    xyzs[i] = {
        x: x_i,
        y: y_i,
        z: z_i,
    }
end

cards = {}
1.upto(n) do |i, _|
    cards[i] = Set[]
end

xyzs.each do |i, xyz2|
    cards[xyz2[:x]] << xyz2[:y] 
    cards[xyz2[:y]] << xyz2[:x]
end

each_node = each_node = lambda {|&b| cards.each_key(&b) }
each_child = lambda {|k, &b| cards[k].each(&b) }
x = TSort.strongly_connected_components(each_node, each_child)

puts x.size