//DFS     graf neorientat
#include<stdio.h>
#include<vector>
#define N_max 100001
using namespace std;

vector <int> a[N_max];
int  viz[N_max],stv[N_max];
unsigned int n,m,k,comp;
void DFS(int nod);

int main()
{
	unsigned int i,x,y;
	
	freopen("dfs.in","r",stdin);
	freopen("dfs.out","w",stdout);
	scanf("%d%d",&n,&m); //numar de noduri, numar de muchii
	for(i=1;i<=m;++i)  // lista de vecini 
	{
		scanf("%d%d",&x,&y);
		a[x].push_back(y);
		a[y].push_back(x);
	}
	i=1;
	while(k<n)
	{
		comp++;
		for(;viz[i]==1;++i);
		DFS(i);
	}
	printf("%d\n",comp);
	return 0;
}

void DFS(int nod)
{
	unsigned int i;
	viz[nod]=1;k++;
	for(i=0;i<a[nod].size();++i)
		if(viz[a[nod][i]]==0)
			DFS(a[nod][i]);
		
}