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.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Scanner;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.util.*;
import java.math.BigInteger;


public class Main{
    public static FastReader fs = new FastReader();
    static int n,m;
    static ArrayList<Integer>[] adj;
    static boolean[] vis;
    static PrintWriter out = new PrintWriter(System.out);

    static void dfs(int node){
        vis[node] = true;
        for(int ch : adj[node])
            if(!vis[ch])
                dfs(ch);
    }

    static void solve() {
        n = fs.nextInt();m = fs.nextInt();
        vis = new boolean[n];
        adj = new ArrayList[n];
        for(int i = 0; i<n; i++)
            adj[i] = new ArrayList<>();
        for(int i = 0; i<m; i++){
            int x = fs.nextInt()-1,y = fs.nextInt()-1;
            adj[x].add(y);
            adj[y].add(x);
        }
        int count = 0;
        for(int i = 0; i<n; i++){
            if(!vis[i]){
                count += 1;
                dfs(i);
            }
        }
        out.println(count-1);
    }

    public static void main(String[] args) {
        Thread t = new Thread(null,null,"",1 << 28) {
            public void run() {
                int test_case = 1;
                //test_case = fs.nextInt();
                for(int cs = 1; cs <= test_case; cs++) {
                    solve();
                }
                out.close();
            }
        };
        t.start();
        try {
            t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next()
        {
            while (st == null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch (IOException  e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

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

        String nextLine()
        {
            String str = "";
            try
            {
                str = br.readLine();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }

        int [] readintarray(int n) {
            int res [] = new int [n];
            for(int i = 0; i<n; i++)res[i] = nextInt();
            return res;
        }
        long [] readlongarray(int n) {
            long res [] = new long [n];
            for(int i = 0; i<n; i++)res[i] = nextLong();
            return res;
        }
    }

    static int ceil(int x,int y) {
        return (x % y == 0 ? x / y : (x / y +1));
    }

    static long ceil(long x,long y) {
        return (x % y == 0 ? x / y : (x / y +1));
    }

    static int max(int x,int y) {
        return Math.max(x, y);
    }

    static int min(int x,int y) {
        return Math.min(x, y);
    }

    static long max(long x,long y) {
        return Math.max(x, y);
    }

    static long min(long x,long y) {
        return Math.min(x, y);
    }

    static int min(int a []) {
        int x = 1_000_000_00_9;
        for(int i = 0; i<a.length; i++)x = min(x,a[i]);
        return x;
    }

    static int max(int a []) {
        int x = -1_000_000_00_9;
        for(int i = 0; i<a.length; i++)x = max(x,a[i]);
        return x;
    }

    static long min(long a []) {
        long x = (long)3e18;
        for(int i = 0; i<a.length; i++)x = min(x,a[i]);
        return x;
    }

    static long max(long a []) {
        long x = -(long)3e18;
        for(int i = 0; i<a.length; i++)x = max(x,a[i]);
        return x;
    }

    static int power(int x,int y) {
        int res = 1;
        while(y > 0) {
            if( y % 2 == 1)res = (res * x);
            y >>= 1;
            x = (x * x);
        }
        return res;
    }

    static long power(long x,long y) {
        long res = 1;
        while(y > 0) {
            if( y % 2 == 1)res = (res * x);
            y >>= 1;
            x = (x * x);
        }
        return res;
    }

    static long power(long x,long y,long mod) {
        long res = 1;
        x %= mod;
        while(y > 0) {
            if( y % 2 == 1)res = (res * x) % mod;
            y >>= 1;
            x = (x * x) % mod;
        }
        return res;
    }

    static void intsort(int [] a) {
        List<Integer> temp = new ArrayList<Integer>();
        for(int i = 0; i<a.length; i++)temp.add(a[i]);
        Collections.sort(temp);
        for(int i = 0; i<a.length; i++)a[i] = temp.get(i);
    }

    static void longsort(long [] a) {
        List<Long> temp = new ArrayList<Long>();
        for(int i = 0; i<a.length; i++)temp.add(a[i]);
        Collections.sort(temp);
        for(int i = 0; i<a.length; i++)a[i] = temp.get(i);
    }

    static void reverseintsort(int [] a) {
        List<Integer> temp = new ArrayList<Integer>();
        for(int i = 0; i<a.length; i++)temp.add(a[i]);
        Collections.sort(temp);
        Collections.reverse(temp);
        for(int i = 0; i<a.length; i++)a[i] = temp.get(i);
    }

    static void reverselongsort(long [] a) {
        List<Long> temp = new ArrayList<Long>();
        for(int i = 0; i<a.length; i++)temp.add(a[i]);
        Collections.sort(temp);
        Collections.reverse(temp);
        for(int i = 0; i<a.length; i++)a[i] = temp.get(i);
    }


    static void intervalsort(int a [],int start,int end) {
        ArrayList<Integer> temp = new ArrayList<>();
        for(int i = start; i<end; i++)
            temp.add(a[i]);
        Collections.sort(temp);
        for(int i = 0; i<temp.size(); i++)
            a[i+start] = temp.get(i);
    }

    static void intervalsort(long a [],int start,int end) {
        ArrayList<Long> temp = new ArrayList<>();
        for(int i = start; i<end; i++)
            temp.add(a[i]);
        Collections.sort(temp);
        for(int i = 0; i<temp.size(); i++)
            a[i+start] = temp.get(i);
    }

    static void reverseintervalsort(int a [],int start,int end) {
        ArrayList<Integer> temp = new ArrayList<>();
        for(int i = start; i<end; i++)
            temp.add(a[i]);
        Collections.sort(temp);
        Collections.reverse(temp);
        for(int i = 0; i<temp.size(); i++)
            a[i+start] = temp.get(i);
    }

    static void reverseintervalsort(long a [],int start,int end) {
        ArrayList<Long> temp = new ArrayList<>();
        for(int i = start; i<end; i++)
            temp.add(a[i]);
        Collections.sort(temp);
        Collections.reverse(temp);
        for(int i = 0; i<temp.size(); i++)
            a[i+start] = temp.get(i);
    }
}