#include <fstream>
#include <vector>
#include <queue>
#include <algorithm>
#define p int
using namespace std;

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

vector <int> v[200002];
queue <int> q;
//priority_queue < p, vector <p> , greater <p> > Q[102];
int n, x, y, c[100002], aux, k, sursa, cont, m;

int conex () {
    for (int i = 1; i <= n; i++) {
        if (c[i] == 0)
            return i;
    }
    return 0;
}

void bfs (int s) {
    c[s] = 1;
    while (!q.empty()) {
        int size = v[s].size();
        for (int i = 0; i < size; i++) {
            if (c[v[s][i]] == 0) {
                q.push(v[s][i]);
                c[v[s][i]]++;
            }
        }
        //Q[cont].push(s);
        q.pop();
        if (!q.empty())
            bfs(q.front());
    }
}

int main () {
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        fin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    sursa = conex();
    while (sursa) {
        cont++;
        q.push(sursa);
        bfs(sursa);
        sursa = conex();
    }
    fout << cont << '\n';
    /*for (int i = 1; i <= cont; i++) {
        while (!Q[i].empty()) {
            fout << Q[i].top() << " ";
            Q[i].pop();
        }
        fout << '\n';
    }*/
}