#include <iostream>
#include <fstream>

using namespace std;
ifstream in("dfs.in");
ofstream out("dfs.out");

bool viz[400000];
int nr1,urm[400000],vf[400000],lst[400000],x,y,n,m,nr;
void adauga (int x,int y)
{
    nr++;
    vf[nr]=y;
    urm[nr]=lst[x];
    lst[x]=nr;
}

void dfs(int x)
{
    viz[x]=true;
    int p,y;
    p=lst[x];
    while (p!=0){
        y=vf[x];
        if(!viz[y])
            dfs(y);
        p=urm[p];
    }
}

int main()
{
    in>>n>>m;
    for (int i=1;i<=m;i++){
        in>>x>>y;
        adauga(x,y);
        adauga(y, x);
    }
    for (int i=1;i<n;i++)
        if(!viz[i]){
            nr1++;
            dfs(i);
    }
    out<<nr1;
}