#include <fstream>
#define NMAX 100001
using namespace std;
int n,sol[NMAX],viz[NMAX],nviz=0;
ofstream g("dfs.out");
typedef struct nod
{
    int y;
    nod *urm;
}*pNod;
pNod lis[NMAX];
void add(pNod &dest,int val)
{
    pNod p;
    p=new nod;
    p->y=val;
    p->urm=dest;
    dest=p;
}
void dfs(int s)
{
    sol[1]=s;
    viz[s]=1;
    int i,j,c;
    i=j=1;
    do
    {
        c=-1;
        for(pNod p=lis[sol[i]];p!=NULL&&c==-1;p=p->urm)
            if(!viz[p->y])
                c=p->y;
        if(c!=-1)
        {
            j++;
            sol[j]=c;
            viz[c]=1;
            i=j;
        }
        else
            i--;
    }while(i>0);
    nviz+=j;
}
int main()
{
    ifstream f("dfs.in");
    ofstream g("dfs.out");
    int m,x,y,k;
    f>>n>>m;
    for(int i=1;i<=m;++i)
    {
        f>>x>>y;
        add(lis[x],y);
        add(lis[y],x);
    }
    int sol=0,nod;
    while(nviz<n)
    {
        sol++;
        k=0;
        for(int i=1;i<=n&&k==0;++i)
            if(viz[i]==0)
            {
                nod=i;
                k=1;
            }
        dfs(nod);
    }
    g<<sol;
    f.close();
    g.close();
    return 0;
}