#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>

using namespace std;

const int nmax=100005;

vector <int> graph[nmax];
bool visited[nmax];
queue <int> dfsqueue;

int dfs(int start_node)
{
    int cnt=1;
    visited[start_node]=true;
    for(int i=0;i<graph[start_node].size();i++)
    {
        if(visited[graph[start_node][i]]==false)
            cnt+=dfs(graph[start_node][i]);
    }
    return cnt;
}

int main()
{
    freopen("dfs.in", "r", stdin);
    freopen("dfs.out", "w", stdout);
    int n, m;

    scanf("%d%d", &n, &m);
    for(int i=1;i<=m;i++)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    int s=dfs(1);
    int nr_conexe=1;
    while(s!=n)
    {
        int k;
        for(int i=1;i<=n;i++)
        {
            if(visited[i]==false)
            {
                k=i;
                break;
            }
        }
        s+=dfs(k);
        nr_conexe++;
    }
    printf("%d\n", nr_conexe);

    return 0;
}