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

int main()
{
	ifstream fi("dfs.in");
	ofstream fo("dfs.out");

	int m, n;
	
	fi >> n >> m;
	vector<list<int>> graph(n);
	
	for (int i = 0; i < m; i++) {
		int a, b;
		fi >> a >> b;
		a--;
		b--;
		graph[a].push_back(b);
		graph[b].push_back(a);
	}

	vector<bool> visited(n, false);
	stack<int> st;
	int count = 0;
	bool more = false;

	for (int i = 0; i < n; i++) {
		if (!visited[i]) {
			st.push(i);
			visited[i] = true;
			more = true;
			break;
		}
	}

	while(more) {
		more = false;
		count++;

		while (st.size() > 0) {
			int node = st.top();
			st.pop();

			for (int i : graph[node]) {
				if (!visited[i]) {
					st.push(i);
					visited[i] = true;
				}
			}
		}

		for (int i = 0; i < n; i++) {
			if (!visited[i]) {
				st.push(i);
				visited[i] = true;
				more = true;
				break;
			}
		}
	}

	fo << count;

	fi.close();
	fo.close();
	return 0;
}