#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

const int N=100001;
vector<int> a[N];
int n;
bool viz[N];

void citire(){
    int m, x, y;
    in>>n>>m;
    for(int i=0; i<m; i++){
        in>>x>>y;
        a[x].push_back(y);
        a[y].push_back(x);
    }
    in.close();
}

void dfs(int x){
    viz[x]=true;
    for(int i=0; i<a[x].size(); i++){
        int y=a[x][i];
        if(!viz[y]){
            dfs(y);
        }
    }
}

int main()
{
    citire();
    int nr=0;
    dfs(1);
    for(int i=0; i<n; i++){
        if(!viz[i])
            nr++;
    }
    out<<nr;
    return 0;
}