#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;

ifstream fin ("dfs.in");
ofstream fout ("dfs.out");

const int nmax = 1e5+5;
const int mmax = 2e5+5;
int n, m, dady[nmax], rang[nmax];
pair<int,int> v[mmax];

int Find(int node){
    while(dady[node]!=node)node=dady[node];
    return node;
}

void Union(int x, int y){
    if(rang[x] > rang[y]) dady[y]=x;
    else dady[x]=y;
    if(rang[x]==rang[y]) rang[y]++;
}

void Kruskal(){
    int rx, ry, conexe=0, i;
    for(i=1; i<=n; i++)
        dady[i]=i;
    for(i=1; i<=m; i++){
        rx=Find(v[i].first);
        ry=Find(v[i].second);
        if(rx!=ry){
            conexe++;
            Union(rx, ry);
        }
    }
    fout << conexe;
}

int main(){
    ios_base::sync_with_stdio(false);
    int i;
    fin >> n >> m;
    for(i=1; i<=m; i++)
        fin >> v[i].first >> v[i].second;

    Kruskal();
    fin.close();
    fout.close();
    return 0;
}