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: Accepted)

N,M = gets.split(' ').map(&:to_i)
@xy = M.times.map{ gets.split(' ').map(&:to_i) }

@xy.sort_by!{|x| x[0]}

@parent = Array.new(N+1,&:itself)
@rank = Array.new(N+1,0)
#puts @parent

def anc(x)
  #puts "x=#{x}"
  #puts "parent[2]=#{@parent[2]}"
  if @parent[x]==x
    return x
  else
    #puts "x=#{x}"
    x=anc(@parent[x])
  end
  return x
end


M.times do |i|
  x=@xy[i][0]
  y=@xy[i][1]
  x_can = anc(x)
  y_can = anc(y)
  #puts "x_can=#{x_can},y_can=#{y_can}"
=begin
  if x_can<y_can
    senzo=x_can
  else
    senzo=y_can
  end
=end
  if @rank[x_can]>=@rank[y_can]
    @parent[y_can]=x_can
    @rank[x_can]+=1 if @rank[x_can]==@rank[y_can]
  else
    @parent[x_can]=@parent[y_can]
  end
  #@parent[x]=senzo
  #@parent[y]=senzo
  #puts @parent
  #puts "aaa"
end
ans = 0
for i in 0..N-1
  cnt = N-i
  senzo = anc(cnt)
  @parent[senzo] = senzo
  if senzo==cnt
    ans+=1
  end
end
puts ans

#puts @parent