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

void show_mat (vector< vector<int> > &mat, const int &n, ostream &out) {
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      out << mat[i][j] << ' ';
    }
    out << '\n';
  }
  out << '\n';
}

int main (int argc, char const *argv[])
{
  ifstream in ("dfs.in");
  
  int n, m; in >> n >> m;
  
  vector < vector<int> > matAdi(n, vector<int>(n));
  
  for (int i = 0; i < m; i++) {
    int x, y; in >> x >> y;
    x--; y--;
    matAdi[x][y] = matAdi[y][x] = 1;
  }
  
  in.close();
  
  set<int> remaining;
  
  for (int i = 0; i < n; i++) {
    remaining.insert(i);
  }
  
  int nr = 0;
  
  queue<int> bfs;
  while (!remaining.empty()) {
    bfs.push(*remaining.begin());
    remaining.erase(remaining.begin());
    
    while (!bfs.empty()) {
      int nod = bfs.front();
      bfs.pop();
      
      for (int i = 0; i < n; i++) {
        if (matAdi[nod][i] && remaining.find(i) != remaining.end()) {
          bfs.push(i);
          remaining.erase(i);
        }
      }
    }
    nr++;
  }
  
  ofstream out ("dfs.out");
  out << nr << '\n';
  out.close();
  
  return 0;
}