#include <iostream>
#include <fstream>
#include <vector>
#define lim 100000
using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");
vector <int> Muchii[lim];

int x,y,n,m,s=1;
int viz[lim];

void dfs (int nod,int s)
{
	viz[nod]=s;
	for (int i=0;i<Muchii[nod].size();i++)
		if (viz[Muchii[nod][i]]==0)
		{
			dfs(Muchii[nod][i],s);
		}
}

int main()
{
	f>>n>>m;
	for (int i=1;i<=m;i++)
	{
		f>>x>>y;
		Muchii[y].push_back(x);
		Muchii[x].push_back(y);
	}
	for (int j=1;j<=n;j++)
		if (viz[j]==0)
		{
			dfs(j,s);
			s++;
		}
	g<<s-1;
	f.close();
	g.close();
	return 0;
}