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

vector<int> a[100000];
int n, m, v[100000], k=1;

void citire()
{
	int i, x, y;
	ifstream in("dfs.in");
	in>>n>>m;
	for (i=0;i<m;++i)
	{
		in>>x>>y;
		a[x].push_back(y);
		a[y].push_back(x);
	}
	in.close();
}

void dfs(int nod)
{
	v[nod] = k;
	vector<int>::iterator i = a[nod].begin(), end = a[nod].end();
	while (i != end)
	{
		if (v[*i] != k)
			dfs(*i);
		++i;
	}
}

int main()
{
	citire();
	for (int i=1; i<=n; ++i)
		if (!v[i])
		{
			dfs(i);
			++k;
		}
	ofstream out("dfs.out");
	out<<k-1;
}