#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <cstring>
using namespace std;
vector <int> vec[100002];
vector <int>::iterator ii;
queue <int> st;
int m,n,unused[100002];
int main()
{
    ifstream fin ("dfs.in");
    ofstream fout ("dfs.out");
    fin>>n>>m;
    int i,x,y;
    memset(unused,0,sizeof(unused));
    for(i=0; i<m; ++i)
    {
        fin>>x>>y;
        vec[x].push_back(y);
        vec[y].push_back(x);
    }
    x=0,y=1;///x=nr de elem conexe
       while(y<=n)
    {
        ++x;
        st.push(y);
        unused[y]=1;

        while(!st.empty())
        {
            int a=st.front();
            st.pop();
            ii=vec[a].begin();
            while(ii!=vec[a].end())
            {
                if(!unused[*ii])
                    unused [*ii]=1,st.push(*ii);

                ++ii;
            }
        }

        while(unused[y])++y;
    }
    fout<<x;
    return 0;
}