Ujan has a lot of useless stuff in his drawers, a considerable part of which are his math notebooks: it is time to sort them out. This time he found an old dusty graph theory notebook with a description of a graph.

It is an undirected weighted graph on n vertices. It is a complete graph: each pair of vertices is connected by an edge. The weight of each edge is either 0 or 1; exactly m edges have weight 1, and all others have weight 0.

Since Ujan doesn't really want to organize his notes, he decided to find the weight of the minimum spanning tree of the graph. (The weight of a spanning tree is the sum of all its edges.) Can you find the answer for Ujan so he stops procrastinating?

Input

The first line of the input contains two integers n and m (1 ≤ n ≤ 10^5, 0 ≤ m ≤ min((n(n-1))/(2),10^5)), the number of vertices and the number of edges of weight 1 in the graph. 

The i-th of the next m lines contains two integers a_i and b_i (1 ≤ a_i, b_i ≤ n, a_i ≠ b_i), the endpoints of the i-th edge of weight 1.

It is guaranteed that no edge appears twice in the input.

Output

Output a single integer, the weight of the minimum spanning tree of the graph.

Examples

Input


6 11
1 3
1 4
1 5
1 6
2 3
2 4
2 5
2 6
3 4
3 5
3 6


Output


2


Input


3 0


Output


0

Note

The graph from the first sample is shown below. Dashed edges have weight 0, other edges have weight 1. One of the minimum spanning trees is highlighted in orange and has total weight 2.

<image>

In the second sample, all edges have weight 0 so any spanning tree has total weight 0.
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;
import java.util.*;
import java.io.*;
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
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////////                                                                                                               /////////
////////                                                                                                               /////////
////////   HHHH        HHHH  EEEEEEEEEEEEE   MMMM          MMMM         OOOOOO             SSSSSSS      EEEEEEEEEEEEE  /////////
////////   HHHH        HHHH  EEEEEEEEEEEEE   MMMMMM      MMMMMM      OOO      OOO        SSSS   SSS     EEEEEEEEEEEEE  /////////
////////   HHHH        HHHH  EEEEE           MMMM MMM  MMM MMMM    OOO          OOO    SSSS       SSS   EEEEE          /////////
////////   HHHH        HHHH  EEEEE           MMMM  MMMMMM  MMMM   OOO            OOO   SSSS             EEEEE          /////////
////////   HHHH        HHHH  EEEEE           MMMM          MMMM  OOO              OOO   SSSSSSS         EEEEE          /////////
////////   HHHHHHHHHHHHHHHH  EEEEEEEEEEE     MMMM          MMMM  OOO              OOO      SSSSSS       EEEEEEEEEEE    /////////
////////   HHHHHHHHHHHHHHHH  EEEEEEEEEEE     MMMM          MMMM  OOO              OOO         SSSSSSS   EEEEEEEEEEE    /////////
////////   HHHH        HHHH  EEEEE           MMMM          MMMM   OOO            OOO              SSSS  EEEEE          /////////
////////   HHHH        HHHH  EEEEE           MMMM          MMMM    OOO          OOO     SSS       SSSS  EEEEE          /////////
////////   HHHH        HHHH  EEEEEEEEEEEEE   MMMM          MMMM      OOO      OOO        SSS    SSSS    EEEEEEEEEEEEE  /////////
////////   HHHH        HHHH  EEEEEEEEEEEEE   MMMM          MMMM         OOOOOO             SSSSSSS      EEEEEEEEEEEEE  /////////
////////                                                                                                               /////////
////////                                                                                                               /////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

public class Contest1 {
    static TreeSet<Integer>[]adj;
    public static void main(String[] args) throws IOException {
        Scanner sc = new Scanner(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int[]c=new int[n];
        adj=new TreeSet[n];
        for (int i =0;i<n;i++)adj[i]=new TreeSet<>();
        UnionFind set= new UnionFind(n);
        while (m-->0){
            int u = sc.nextInt()-1;
            int v = sc.nextInt()-1;
            if (u<v){
                adj[u].add(v);
            }
            else adj[v].add(u);
        }
        for (int i =0;i<n;i++){
            int nxt=-1;
            for (int j=i+1;j<n;j++){
                if (!adj[i].contains(j)){
                    nxt=j;
                    break;
                }
            }
//            System.out.println(nxt+" "+i+" "+adj[i]);
            if (nxt!=-1){
                TreeSet<Integer>remove=new TreeSet<>();
                for (int x:adj[i]){
                    if (adj[nxt].contains(x))remove.add(x);
                }
                adj[nxt]=remove;
                set.unionSet(i,nxt);
            }
        }
        pw.println(set.numSets-1);
        pw.flush();
    }

    static long gcd(long a, long b) {
        if (a == 0) return b;
        return gcd(b % a, a);
    }
    static class UnionFind {
        int[] p, rank, setSize;
        int numSets;

        public UnionFind(int N)
        {
            p = new int[numSets = N];
            rank = new int[N];
            setSize = new int[N];
            for (int i = 0; i < N; i++) {  p[i] = i; setSize[i] = 1; }
        }

        public int findSet(int i) { return p[i] == i ? i : (p[i] = findSet(p[i])); }

        public boolean isSameSet(int i, int j) { return findSet(i) == findSet(j); }

        public void unionSet(int i, int j)
        {
            if (isSameSet(i, j))
                return;
            numSets--;
            int x = findSet(i), y = findSet(j);
            if(rank[x] > rank[y]) { p[y] = x; setSize[x] += setSize[y]; }
            else
            {	p[x] = y; setSize[y] += setSize[x];
                if(rank[x] == rank[y]) rank[y]++;
            }
        }

        public int numDisjointSets() { return numSets; }

        public int sizeOfSet(int i) { return setSize[findSet(i)]; }
    }
    static class Scanner {
        StringTokenizer st;
        BufferedReader br;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public Scanner(FileReader r) {
            br = new BufferedReader(r);
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens())
                st = new StringTokenizer(br.readLine());
            return st.nextToken();
        }

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

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

        public String nextLine() throws IOException {
            return br.readLine();
        }

        public double nextDouble() throws IOException {
            String x = next();
            StringBuilder sb = new StringBuilder("0");
            double res = 0, f = 1;
            boolean dec = false, neg = false;
            int start = 0;
            if (x.charAt(0) == '-') {
                neg = true;
                start++;
            }
            for (int i = start; i < x.length(); i++)
                if (x.charAt(i) == '.') {
                    res = Long.parseLong(sb.toString());
                    sb = new StringBuilder("0");
                    dec = true;
                } else {
                    sb.append(x.charAt(i));
                    if (dec)
                        f *= 10;
                }
            res += Long.parseLong(sb.toString()) / f;
            return res * (neg ? -1 : 1);
        }

        public boolean ready() throws IOException {
            return br.ready();


        }
    }
}