#include<iostream>
#include<fstream>
#include<string>
#include<vector>
#include<queue>
#include<stack>
using namespace std;


class Graf
{

private:

	int nr_noduri;
	int nr_muchii;
	vector<int>init;
	vector<int>fin;
	

public:

	Graf(){}

	void citire_graf_dfs() {

		ifstream f("dfs.in");
		int x, y;
		f >> nr_noduri;
		f >> nr_muchii;

		while (f >> x >> y) {

			init.push_back(x);
			fin.push_back(y);
		}


		f.close();
	}

	void citire_graf_bfs() {
		

		int start;
		ifstream f("bfs.in");
		int x, y;
		f >> nr_noduri;
		f >> nr_muchii;
		f >> start;

		while (f >> x >> y) {

			init.push_back(x);
			fin.push_back(y);
		}
	}

	int get_nr_noduri() { return nr_noduri; }
	void set_nr_noduri(int n) { nr_noduri = n; }

	int get_nr_muchii() { return nr_muchii; }
	void set_nr_muchii(int m) { nr_muchii = m; }


	string get_muchii() {
		
		string text;

		int i;
		for (i = 0; i < nr_muchii * 2; i++) {

			text += "\n" + to_string(init[i]) + " " + to_string(fin[i]);

		}
		
		return text;
	}


	void bfs1(int start) {

		vector<int> vizit;
		for (int i = 0; i <= nr_noduri; i++) { vizit.push_back(-1); }

		queue<int>coada;
		int x;

		//cout << start << ", ";
		coada.push(start);
		vizit[start] = 0;

		while (!coada.empty()) {

			x = coada.front();
			coada.pop();

			for (int i = 0; i < nr_muchii; i++) {

				if (init[i] == x && vizit[fin[i]] == -1) {
					coada.push(fin[i]);

					vizit[fin[i]] = vizit[init[i]] + 1;
				}
			}
		}

		ofstream g("bfs.out");
		for (int i = 1; i <= nr_noduri; i++) {

			g << vizit[i] << " ";
		}
		g.close();
	}


	void bfs2(int start) {

		vector<vector<int>> lista;
		lista.resize(get_nr_noduri() + 1);

		for (int i = 0; i < nr_muchii; i++) {

			lista[init[i]].push_back(fin[i]);
		}

		queue<int>coada;
		int x;

		vector<int> vizit;
		for (int i = 0; i <= nr_noduri; i++) { vizit.push_back(-1); }

		coada.push(start);
		vizit[start] = 0;

		while (!coada.empty()) {

			x = coada.front();
			coada.pop();

			for (int i = 0; i < lista[x].size(); i++) {

				if (vizit[lista[x][i]] == -1) {

					coada.push(lista[x][i]);
					vizit[lista[x][i]] = vizit[x] + 1;
				}
			}
		}

		ofstream g("bfs.out");
		for (int i = 1; i <= nr_noduri; i++) {

			g << vizit[i] << " ";
		}
		g.close();
	}

	void dfs(int start, vector<int>& vizit) {

		int v;
		vector<vector<int>> lista;
		lista.resize(get_nr_noduri() + 1);

		for (int i = 0; i < nr_muchii ; i++) {

			lista[init[i]].push_back(fin[i]);
			lista[fin[i]].push_back(init[i]);
		}

		stack<int>st;
		int x;


		st.push(start);
		vizit[start] = 1;

		while (!st.empty()) {

			x = st.top();
			v = 0;


			for (int i = 0; i < lista[x].size(); i++) {


				if (vizit[lista[x][i]] == 0) {

					v = lista[x][i];
					break;
				}
			}

			if (v == 0) { st.pop(); }
			else {
				st.push(v);
				vizit[v] = 1;
			}
		}
	}


	bool check_vizit(vector<int>vizit) {

		for (int i = 1; i <= nr_noduri; i++)
			if (vizit[i] == 0)
				return false;

		return true;
	}

	void comp_conexe() {

		vector<int> vizit;
		for (int i = 0; i <= nr_noduri; i++) { vizit.push_back(0); }

		int count = 0;
		
		for (int i = 1; i < nr_noduri && check_vizit(vizit) == false; i++) {

			if (vizit[i] == 0) {

				dfs(i, vizit);
				count++;
			}
			
		}

		ofstream g("dfs.out");
		g << count;
		g.close();
	}


	void citire_ST() {

		ifstream f("sortaret.in");
		int x, y;
		f >> nr_noduri;
		f >> nr_muchii;

		while (f >> x >> y) {

			init.push_back(x);
			fin.push_back(y);
		}

		f.close();
	}


};

int main() {

	Graf* g = new Graf;

	g->citire_graf_dfs();
	g->comp_conexe();


	return 0;
}