#include<iostream>
#include<fstream>
#include<vector>
using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");
int viz[100000];
vector <int> v[100000];
void dfs(int nod)
{
	viz[nod] = 1;
	for (int i = 0; i < v[nod].size(); i++)
		if (!viz[v[nod][i]])
			dfs(v[nod][i]);
}

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