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

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

int N, M, vizitat[100005], indice_componenta = 1;

vector<int> G[100005];

void DFS(int nod, int indice_componenta)
{
    vizitat[nod] = indice_componenta;
    for (int i = 0; i < G[nod].size(); i++)
    {
        int ngb = G[nod][i];
        if (vizitat[ngb] == 0)
            DFS(ngb, indice_componenta);
    }
}

int main()
{
    fin >> N >> M;
    for (int i = 1; i <= M; i++)
    {
        int nod1, nod2;
        fin >> nod1 >> nod2;
        G[nod1].push_back(nod2);
        G[nod2].push_back(nod1);
    }
    for (int i = 1; i <= N; i++)
    {
        if (vizitat[i] == 0)
        {
            DFS(i, indice_componenta);
            indice_componenta++;
        }
    }
    fout << indice_componenta - 1  << "\n";
    return 0;
}