#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;

#define maxN 100005

int N , M , comp_conex = 0;
bool conex[maxN];

vector <int> lista[maxN];

void dfs (int nod)
{
	for (int i = nod ; i <= N ; ++i)
	{
		if (!conex[nod])
		{
			comp_conex++;
			conex[nod] = 1;
		}
		
		for (unsigned j = 0 ; j < lista[nod].size () ; ++j)
			conex[lista[nod][j]] = 1;
		
		dfs (i + 1);
	}
	
}
int main ()
{
	int x , y;
	
	freopen ("dfs.in" , "r" , stdin);
	freopen ("dfs.out" , "w" , stdout);
	
	scanf ("%d %d" , &N , &M);
	
	for (int i = 1 ; i <= M ; ++i)
	{
		scanf ("%d %d" , &x , &y);
		
		lista[x].push_back (y);
		lista[y].push_back (x);
	}
	
	dfs (1);
	
	printf ("%d" , comp_conex);
	
	return 0;
}