#include <iostream>
#include <fstream>
#include <vector>
#define NLIM 100005

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

bool viz[NLIM] = { false };
vector<int> Muchii[NLIM];

void citire(int &n, int &m) {
    f >> n >> m;
    for(int i=0; i<m; i++) {
        int s, d;
        f >> s >> d;
        Muchii[s].push_back(d);
        Muchii[d].push_back(s);
    }
}

void DFS(int nod) {
    viz[nod] = 1;
    for(unsigned int i=0; i<Muchii[nod].size(); i++) {
        int vecin = Muchii[nod][i];
        if(!viz[vecin])
            DFS(vecin);
    }
}

int main() {
    int n, m, insule = 0;
    citire(n, m);

    for(int i=1; i<n; i++) {
        if(viz[i]) continue;
        insule++;
        DFS(i);
    }

    g << insule << '\n';
    return 0;
}