#include<stdio.h>
#include <vector>
#include <queue>
using namespace std;

long nrg,i,n,m,nr,x,y,mina,mark[100001];

vector<long> a[100001]; 
queue<long> q;

int main()
{
	freopen("dfs.in","r",stdin);
	freopen("dfs.out","w",stdout);
	scanf("%ld %ld",&n,&m);
	for(i=1;i<=m;i++)
	{
		scanf("%ld %ld",&x,&y);
		a[y].push_back(x);
		a[x].push_back(y);
	}
	mina=1;
	while(mina<=n)
	{
		for(i=mina;i<=n;i++) 
			if(mark[i]==0)
			{
				mina=i;
				break;
			}
		if(mark[mina]==1) break;
		nrg++;
		
		mark[mina]=1;
		q.push(mina);
		while(!q.empty())
		{
			x=q.front();
			nr=a[x].size();
			for(i=0;i<nr;i++)
				if(mark[a[x][i]]==0)
				{
					mark[a[x][i]]=1;
					q.push(a[x][i]);
				}
			q.pop();
		}
		
	}
	printf("%ld\n",nrg);
	return 0;
}