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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

public class Hello
{
    private const int MOD_N = 1000000000 + 7;

    public static void Main()
    {
        var list = Console.ReadLine().Split(' ');
        var n = int.Parse(list[0]);
        var m = int.Parse(list[1]);

        var maps = new List<int>[n];
        for (int i = 0; i < maps.Length; ++i)
            maps[i] = new List<int>();

        for (; m > 0; --m)
        {
            var list2 = Console.ReadLine().Split(' ');
            var x = int.Parse(list2[0]) - 1;
            var y = int.Parse(list2[1]) - 1;
            maps[x].Add(y);
            maps[y].Add(x);
        }

        var flags = new bool[n];
        var candidates = new List<int>();

        int ans = 0;

        for (int i = 0; i < flags.Length; ++i)
        {
            if (flags[i])
                continue;
            flags[i] = true;
            ++ans;

            candidates.Add(i);
            do
            {
                var index = candidates.Count - 1;
                var c = candidates[index];
                candidates.RemoveAt(index);
                var map = maps[c];
                for (int j = 0, count = map.Count; j < count; ++j)
                {
                    var mp = map[j];
                    if (flags[mp])
                        continue;
                    flags[mp] = true;
                    candidates.Add(mp);
                }
            } while (candidates.Count > 0) ;
        }

        Console.WriteLine(ans);
    }
}