#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

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

vector <vector <int>> v;
vector <bool> visited;
int n, m, cnt = 1;

void read() {
    f >> n >> m;
    v = vector <vector <int>> (n + 1);
    visited = vector <bool> (n + 1);
    int x, y;
    for(int i = 1; i <= m; ++i) {
        f >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
}

void dfs(int node) {
    visited[node] = true;
    for(const int& neighbour : v[node])
        if(!visited[neighbour])
            dfs(neighbour);
}

int main()
{
    read();
    dfs(1);
    for(int i = 2; i <= n; ++i)
        if(!visited[i])
            dfs(i), ++cnt;
    g << cnt;
}