#include <fstream>
#include <set>
using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");
set<int> v[100005];
int n, m, x, y, k = 1;
bool viz[100005];
void dfs(int x, int y) {
  viz[x] = y;
  for (set<int>::iterator it = v[x].begin(); it != v[x].end(); it++) {
	  if (!viz[*it]) {
		  dfs(*it, y);
	  }
  }
}
int main() {
	f >> n >> m;
	for (int i = 1; i <= m; i++) {
		f >> x >> y;
		v[x].insert(y);
		v[y].insert(x);
    }
	for (int i = 1; i <= n; i++) {
		if (viz[i] == 0) {
			dfs(i, k);
			k++;
		}
	}
	g << k - 1;
	return 0;
}