#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <unordered_map>
using namespace std;
ifstream in("dfs.in");
ofstream out("dfs.out");
int n,m,i,j,x,y,nr=0,val;
unordered_map<int,bool> p;
queue<int> q;
int main()
{
    in>>n>>m;
    vector<int> v[n+1];
    for(i=1;i<=n;i++)
        p[i] = true;
    for(i=0;i<m;i++)
    {
        in>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
    }

    while(p.size()>0)
    {
        unordered_map<int,bool>::iterator it = p.begin();
        q.push(it->first);
        p.erase(it->first);
        while(!q.empty())
        {
            val = q.front();
            q.pop();
            for(vector<int>::iterator ite = v[val].begin();ite!=v[val].end();ite++)
            {
                auto iter = p.find(*ite);
                if (iter != p.end())
                {
                    q.push(*ite);
                    p.erase(*ite);
                }
            }
        }
        nr++;
    }
    out<<nr;
    return 0;
}