#include <stdio.h>
#include <vector>
#define NMAX 100023
FILE *fin, *fout;
int n, m, x, y, viz[NMAX], pos = 1;
std::vector<int> adj[NMAX];
void dfs(int a, int b)
{
	if(viz[a]) return;
	viz[a] = b;
	int sizen = adj[a].size();
	for(int i = 0; i< sizen; i++)
	{
		dfs(adj[a][i], b);
	}
}
int main()
{
	fin = freopen("dfs.in", "r", stdin);
	fout = freopen("dfs.out", "w", stdout);
	scanf("%d%d", &n, &m);
	for(int i = 0; i< m; i++)
	{
		scanf("%d%d", &x, &y);
		adj[x].push_back(y);
		adj[y].push_back(x);
	}
	for(int i = 1; i<= n; i++)
	{
		if(viz[i]) continue;
		dfs(i, pos);
		pos++;
	}
	printf("%d\n", pos-1);
	fclose(fin);
	fclose(fout);
	return 0;
}