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.*;
import java.util.*;
public class Main {
    final static long mod = 1000000007;
    static class Edge {
        int from, to, cost;

        public Edge(int from, int to, int cost) {
            this.from = from;
            this.to = to;
            this.cost = cost;
        }
    }

    // Perform a depth first search on the graph counting
    // the number of nodes traversed starting at some position
    static long dfs(int at, boolean[] visited, Map<Integer, List<Edge>> graph) {

        // We have already visited this node
        if (visited[at]) return 0;

        // Visit this node
        visited[at] = true;
        long count = 1;

        // Visit all edges adjacent to where we're at
        List<Edge> edges = graph.get(at);
        if (edges != null) {
            for (Edge edge : edges) {
                count += dfs(edge.to, visited, graph);
            }
        }

        return count;
    }

    public static void addDirectedEdge(Map<Integer, List<Edge>> graph, int from, int to, int cost) {
        List<Edge> list = graph.computeIfAbsent(from, k -> new ArrayList<Edge>());
        list.add(new Edge(from, to, cost));
    }
    static void debug(Object...args)
    {
        System.out.println(Arrays.deepToString(args));
    }
    public static void main(String[] args) {
        InputReader sc = new InputReader(System.in);
        PrintWriter pw = new PrintWriter(System.out);
        Random gen = new Random();
        int test = 1;//sc.nextInt();
        while(test-->0) {

            int n = sc.nextInt();
            int m = sc.nextInt();
            HashMap<Integer,List<Edge>> graph = new HashMap<>();
            for(int i=0;i<m;i++)
            {
                int from = sc.nextInt();
                int to = sc.nextInt();
                addDirectedEdge(graph,from-1,to-1,0);
                addDirectedEdge(graph,to-1,from-1,0);
            }
//        for(Integer i  :graph.keySet())
//        {
//            List<Edge> l = graph.get(i);
//            for(Edge e : l)
//                pw.println(e.from + " "+e.to + " "+ e.cost);
//        }
            boolean [] visited = new boolean[n];
            long count = 1;
            HashMap<Long,Long> map = new HashMap<>();
            for(int i=0;i<n;i++)
            {
                if(!visited[i])
                {
                    long c = dfs(i,visited,graph);
                    map.put(count,c);
                    count++;

                }
            }
            pw.println(map.size()-1);
//        pw.println("************************");
//        debug(map.toString());


        }
        pw.flush();
        pw.close();

    }




















































































































































































    static class Data implements Comparable<Data>{
        int x;
        int y;

        public Data (int m, int n) {
            x = m;
            y = n;
        }
        @Override
        public int compareTo(Data o) {
            return y - o.y;
        }
    }

    static class InputReader {

        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, snumChars;

        public InputReader(InputStream st) {
            this.stream = st;
        }

        public int read() {
            if (snumChars == -1)
                throw new InputMismatchException();
            if (curChar >= snumChars) {
                curChar = 0;
                try {
                    snumChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (snumChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public int[] nextIntArray(int n) {
            int [] a = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = nextInt();
            }
            return a;
        }
        public long[] nextLongArray(int n) {
            long [] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = nextLong();
            }
            return a;
        }

        public static int[] shuffle(int[] a, Random gen)
        { for(int i = 0, n = a.length;i < n;i++)
        { int ind = gen.nextInt(n-i)+i;
            int d = a[i];
            a[i] = a[ind];
            a[ind] = d;

        }
            return a;
        }
        public static char[] shuffle(char[] a, Random gen)
        { for(int i = 0, n = a.length;i < n;i++)
        { int ind = gen.nextInt(n-i)+i;
            char d = a[i];
            a[i] = a[ind];
            a[ind] = d;

        }
            return a;
        }


        public String readString() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public String nextLine() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isEndOfLine(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        private boolean isEndOfLine(int c) {
            return c == '\n' || c == '\r' || c == -1;
        }

    }

}
