백준 2606

import java.util.*;
public class Main {

	public static boolean visited [];
	public static int map[][];
	
	public static int n;
	
	public static int res=0;
	public static void main(String[] args) {
	
		Scanner sc=new Scanner(System.in);
		
		n=sc.nextInt();	 //정점의 갯수 	
		int m=sc.nextInt(); //간선의 갯수
		 
		
		map=new int[n+1][n+1];
		visited=new boolean[n+1];
		 
		Arrays.fill(visited, false); //visited 배열을 모두 false로 초기화
		for(int i=0; i<n+1;i++){
			Arrays.fill(map[i], 0);
		}
		for(int i=0;i<m;i++) {
			int a=sc.nextInt();	  
			int b=sc.nextInt();			
			map[a][b]=1;
			map[b][a]=1;  
		}
		 
		dfs(1);
		 
		System.out.println(res-1);
	}
	public static void dfs(int k) {
		res++;
		visited[k]=true;
		for(int i=0;i<n+1;i++) {
			if(visited[i]==false&&map[k][i]==1) {
				dfs(i);
			}
		}
	}
}