There are N cities numbered 1 through N, and M bidirectional roads numbered 1 through M. Road i connects City A_i and City B_i.

Snuke can perform the following operation zero or more times:

* Choose two distinct cities that are not directly connected by a road, and build a new road between the two cities.



After he finishes the operations, it must be possible to travel from any city to any other cities by following roads (possibly multiple times).

What is the minimum number of roads he must build to achieve the goal?

Constraints

* 2 \leq N \leq 100,000
* 1 \leq M \leq 100,000
* 1 \leq A_i < B_i \leq N
* No two roads connect the same pair of cities.
* All values in input are integers.

Input

Input is given from Standard Input in the following format:


N M
A_1 B_1
:
A_M B_M


Output

Print the answer.

Example

Input

3 1
1 2


Output

1
import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Map.Entry;

import java.util.PriorityQueue;
import java.util.Random;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;


public class Main {
	
	public static class UnionFind {
		int[] par; //

		public UnionFind(int n) {
			par = new int[n];
			for(int i = 0; i < n; i++){
				par[i] = -1;
			}
		}

		public int find(int x) {
			if(par[x] < 0){
				return x;
			}else{
				return par[x] = find(par[x]);
			}
		}

		public boolean union(int x, int y) {
			x = find(x);
			y = find(y);

			if(x != y){
				if(par[y] < par[x]){ // 多い方が根になるようにスワップする.
					int tmp = x;
					x = y;
					y = tmp;
				}
				par[x] += par[y];
				par[y] = x;
				return true;
			}else{
				return false;
			}
		}

		public boolean same(int x, int y) {
			return find(x) == find(y);
		}

		public int size(int x) {
			return -par[find(x)];
		}
	}
	
	public static void main(String[] args) throws IOException {	
		try(final Scanner sc = new Scanner(System.in)){
			final int N = sc.nextInt();
			final int M = sc.nextInt();
			
			UnionFind uf = new UnionFind(N);
			
			for(int i = 0; i < M; i++) {
				final int a = sc.nextInt() - 1;
				final int b = sc.nextInt() - 1;
				
				uf.union(a, b);
			}
			
			HashSet<Integer> groups = new HashSet<Integer>();
			for(int i = 0; i < N; i++) {
				groups.add(uf.find(i));
			}
			
			System.out.println(groups.size() - 1);
			
		}
	}

	public static class Scanner implements Closeable {
		private BufferedReader br;
		private StringTokenizer tok;

		public Scanner(InputStream is) throws IOException {
			br = new BufferedReader(new InputStreamReader(is));
		}

		private void getLine() throws IOException {
			while(!hasNext()){
				tok = new StringTokenizer(br.readLine());
			}
		}

		private boolean hasNext() {
			return tok != null && tok.hasMoreTokens();
		}

		public String next() throws IOException {
			getLine();
			return tok.nextToken();
		}

		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}

		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}
		

		public double nextDouble() throws IOException {
			return Double.parseDouble(next());
		}

		public int[] nextIntArray(int n) throws IOException {
			final int[] ret = new int[n];
			for(int i = 0; i < n; i++){
				ret[i] = this.nextInt();
			}
			return ret;
		}

		public long[] nextLongArray(int n) throws IOException {
			final long[] ret = new long[n];
			for(int i = 0; i < n; i++){
				ret[i] = this.nextLong();
			}
			return ret;
		}

		public void close() throws IOException {
			br.close();
		}
	}
}
