#include <iostream>
#include <stdio.h>
#include <vector>
#include <string.h>


FILE *f=fopen("dfs.in","r");
FILE *g=fopen("dfs.out","w");

using namespace std;
vector <int> v[100010];

int nr,w[100010],n,m,nod,i,x,y,viz[100010];

void dfs(int nod)
{
    int i,j,l;
    viz[nod]=1;
   for(i=1;i<=n;i++)
   {
       viz[i]=1;
       nr++;
       for(j=0;j<w[i];j++)
       if(viz[v[i][j]]){nr--;break;} else viz[v[i][j]]=1;
   }

}

int main()
{
    fscanf(f,"%d%d",&n,&m);
    for(i=1;i<=m;i++)
    {
        fscanf(f,"%d%d",&x,&y);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    for(i=1;i<=n;i++)
    w[i]=v[i].size();
    dfs(nod);
    fprintf(g,"%d",nr);
    fclose(g);
    return 0;
}