#include <fstream>
#include <vector>
using namespace std;

vector<int> a[200000];
int n, m, v[200000], k=1;

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

void dfs(int nod)
{
    v[nod] = k;
    vector<int>::iterator i = a[nod].begin();//, end = a[nod].end();
    while (i != a[nod].end())
    {
        if (v[*i] != k)
            dfs(*i);
        ++i;
    }
}

int main()
{
    citire();
    for (int i=1; i<=n; ++i)
        if (!v[i])
        {
            dfs(i);
            ++k;
        }
    ofstream out("dfs.out");
    out<<k-1;
}