#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int viz[100001],n,m,s;
vector<int> G[100001];
void dfs(int x, int aux)
{
    viz[x]=aux;
    for(vector<int>::iterator it=G[x].begin();it!=G[x].end();it++)
    {
        if(viz[*it]==0)
            dfs(*it,aux);
    }
}
int main()
{
	fin >> n >> m;
	for(int i=1;i<=m;i++)
    {
        int x,y;
        fin >> x >> y;
        G[x].push_back(y);
        G[y].push_back(x);
    }
    int aux=1;
    for(int i=1;i<=n;i++)
    {
        if(viz[i]==0)
        {
            viz[i]=aux;
            dfs(i,aux);
            aux++;
        }
    }
    aux--;
    fout << aux;
	return 0;
}