#include <cstdio>
#include <stack>
#include <queue>
#include <algorithm>
FILE *f=fopen("dfs.in","r");
FILE *g=fopen("dfs.out","w");
using namespace std;

#define x first
#define y second
#define mp make_pair

struct nod{
    int v;
    nod *next;
};
typedef nod *lista;

stack <int> s;
queue <int> q;
pair <int,int> vrtx[200001];

int n,m,used[100001];
lista lv[100001];

void get_GRAPH()
{
    fscanf(f,"%d%d",&n,&m);
    int i,a,b;
    lista p;
    for(i=1;i<=m;++i)fscanf(f,"%d%d",&a,&b), a<b ? vrtx[i] = mp(a,b) : vrtx[i] = mp(b,a);
    sort(vrtx+1,vrtx+m+1);
    for(i=1;i<=m;++i)
        if(vrtx[i].x!=vrtx[i].y&&(vrtx[i-1].x!=vrtx[i].x||vrtx[i-1].y!=vrtx[i].y))
        {
            p=new nod;p->v=vrtx[i].x;p->next=lv[vrtx[i].y];lv[vrtx[i].y]=p;
            p=new nod;p->v=vrtx[i].y;p->next=lv[vrtx[i].x];lv[vrtx[i].x]=p;
        }
}
int pz=0;
int done()
{
    for(int i=1;i<=n;++i)
        if(!used[i]){pz=i;return 0;}
    return 1;
}

void DFS(int k)
{
    lista p;
    int nodc;
    s.push(k);
    used[k]=1;
    while(!s.empty())
    {
        nodc=s.top(),s.pop();
        for(p=lv[nodc];p;p=p->next)
            if(!used[p->v])
            {
                used[p->v]=1;
                s.push(p->v);
            }
    }
}
void BFS(int k)
{
    lista p;
    int nodc;
    q.push(k);
    used[k]=1;
    while(!q.empty())
    {
        nodc=q.front(),q.pop();
        for(p=lv[nodc];p;p=p->next)
            if(!used[p->v])
            {
            used[p->v]=1;
            q.push(p->v);
            }
    }
}
int main()
{
    get_GRAPH();
    int nrg=0;
    while(!done())
    {
        //BFS(pz);
        DFS(pz);
        ++nrg;
    }
    fprintf(g,"%d",nrg);
    return 0;
}