#include <iostream>
#include <vector>
#include <fstream>

using namespace std;

#define MAX_NODURI 10000

ifstream f("in.in");
ofstream g("out.out");

vector<int> graf[MAX_NODURI];
int vizitat[MAX_NODURI];

void DFS(int nod, int val)
{
    if(vizitat[nod] == 0)
    {
        vizitat[nod] = val;
        for(unsigned int i = 0; i < graf[nod].size(); i++)
        {
            DFS(graf[nod][i], val);
        }
    }
}

int main()
{
    int N, M;
    f>>N>>M;
    for(int i = 0; i < M; i++)
    {
        int x, y;
        f>>x>>y;
        graf[x].push_back(y);
        graf[y].push_back(x);
    }
    int k = 1;
    for(int i = 0; i < N; i++)
    {
        if(vizitat[i] == 0)
        {
            DFS(i, k);
            k++;
        }
    }
    cout<<k-1;
    return 0;
}