import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;
import java.lang.Math;

class point {
    int mark=0;           //метка занятости
    int parent=-1;        //корень
    int cap=0;            //число инцидентных ребер
    ArrayList<Integer> list = new ArrayList<Integer>();
}

//кольцевой буфер
class Queue {
    int size,head,tail;
    int[] data;
    Queue(int size) {
        data = new int [this.size = size];
    }
    void add(int value) {
        if (++tail == size)
            tail = 0;
        data[tail] = value;
    }
    int extract() {
        if (++head == size)
            head = 0;
        return data[head];
    }
}

public class BridgeNum {
    public static void main(String[] arg) {
        Scanner sc = new Scanner(System.in);
        int i=0,j=0,n=sc.nextInt(),m=sc.nextInt(),first,second,CompNumber=1;
        point [] graph=new point[n];
        int [] unsorted=new int [n];
        for (i=0;i<n;i++) {
            graph[i]=new point();
            graph[i].mark=0;
            unsorted[i]=i;
        }
        Queue q=new Queue(n+1);
        for(i=0;i<m;i++){
            first=sc.nextInt(); second=sc.nextInt();
            graph[first].cap++;
            graph[first].list.add(second);
            graph[second].cap++;
            graph[second].list.add(first);
        }

        for (i=0;i<n;i++) {
            if (graph[i].mark == 0) {
                CompNumber--;
                VisitVertex1(graph, q, i);
            }
            while (q.head != q.tail)//dfs2
            {
                first = q.extract();
                if (unsorted[first] == first) {
                    unsorted[first]=-1;
                    VisitVertex2(graph, q, first, unsorted);
                    CompNumber++;
                }
            }
        }
        System.out.println(CompNumber-1);
    }

    public static void VisitVertex1(point[] graph, Queue q,int n)
    {
        int timelimit1,timelimit2;
        graph[n].mark=1; //gray
        q.add(n);//Enq
        timelimit1=graph[n].cap;
        for(int i=0;i<timelimit1;i++)
        {
            timelimit2=graph[n].list.get(i);
            if(graph[timelimit2].mark==0)
            {
                graph[timelimit2].parent=n;
                VisitVertex1(graph,q,graph[n].list.get(i));
            }
        }
        graph[n].mark=2;//black
    }

    public static void VisitVertex2(point[] graph, Queue q,int f,int[] unsorted)
    {
        int timelimit1=graph[f].cap;
        unsorted[f]=-1;
        for(int i=0;i<timelimit1;i++)
        {
            int timelimit2=graph[f].list.get(i);
            if(unsorted[timelimit2]!=-1)
                if(graph[timelimit2].parent!=f)
                {
                    VisitVertex2(graph,q,timelimit2,unsorted);
                }
        }
    }

}