#include <fstream>
#include <vector>
#include <bitset>
#define MAX 100005
using namespace std;

ifstream f("dfs.in");
ofstream g("dfs.out");

int n, m, k;
bitset<MAX> viz;
vector<int> G[MAX];

void dfs(int x)
{
	viz[x] = 1;
	for (auto it : G[x])
		if (!viz[it]) dfs(it);
}

int main()
{
	f >> n >> m;
	int x, y;
	for (int i = 0; i < m; i++)
	{
		f >> x >> y;
		G[x].push_back(y);
		G[y].push_back(x);
	}
	dfs(1);
	k++;
	for (int i = 2; i <= n; i++)
		if (!viz[i])
		{
			k++;
			dfs(i);
		}
	g << k;
	return 0;
}