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.util.*;
import java.io.*;
import java.math.BigInteger;
import java.text.*;
public class Main implements Runnable {
    static int mod = 1000_000_007;
    static long lim = (long)1e9 + 6;
    static long mod1 = 998244353;
    static boolean fileIO = false;
    static FastScanner f;
    static int inf = 2000_000_000;
    static PrintWriter pw = new PrintWriter(System.out);
    static Scanner S = new Scanner(System.in);
    static long x0; static long y0;
    static long iinf = (long)(1e18);
    static double eps = (double)1e-4;
    static HashMap<Integer , ArrayList<Integer>> g;
    static boolean vis[];
    static void dfs(int src) {
        vis[src] = true;
        for (Integer node : g.get(src)) {
            if (!vis[node]) {
                dfs(node);
            }
        }
    }
    public static void solve() {
        int n = f.ni(); int m = f.ni();
        g = new HashMap<>();
        vis = new boolean[n + 1];

        for (int i = 1; i <= n; ++i) {
            g.put(i , new ArrayList<Integer>());
        }

        for (int i = 0; i < m; ++i) {
            int u = f.ni(); int v = f.ni();
            g.get(u).add(v);
            g.get(v).add(u);
        }

        int cnt = 0;
        for (int i = 1; i <= n; ++i) {
            if (!vis[i]) {
                ++cnt;
                dfs(i);
            }
        }
        pn(--cnt);
    }    
    public static void main(String[] args)throws IOException {
        new Thread(null , new Main() , "F*uckit" , 1 << 28).start();  
    }
        
/******************************END OF MAIN PROGRAM*******************************************/
    public void run() {
        f = new FastScanner(System.in);
        //pre();
        int t = 1;
        int tt = 1;
        //fw = new FileWriter("!out.txt");
        while(t --> 0) {
            //fw.write("Case #" + (tt++) + ": ");
            //fw.write("\n");
            solve();
        }
        pw.flush(); 
        pw.close();
        //fw.close();  
    }
    public static class FastScanner {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private FastScanner.SpaceCharFilter filter;
 
        public FastScanner(InputStream stream) {
            this.stream = stream;
        }
 
        public int read() {
            if (numChars == -1)
                throw new InputMismatchException();
 
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
 
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }
 
        public int ni() {
            int c = read();
 
            while (isSpaceChar(c))
                c = read();
 
            int sgn = 1;
 
            if (c == '-') {
                sgn = -1;
                c = read();
            }
 
            int res = 0;
            do {
                if (c < '0' || c > '9') throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
 
            return res * sgn;
        }
 
        public long nl() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
 
            do {
                if (c < '0' || c > '9') throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
            return res * sgn;
        }
 
        public String next() {
            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 boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
 
        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }
    public static void pn(Object o){pw.println(o);}
    public static void pi(Object o){pw.print(o);pw.flush();}
    public static void p(Object o){pw.print(o);}
    public static void pni(Object o){pw.println(o);pw.flush();}
    static int gcd(int a,int b){if(b==0)return a;else{return gcd(b,a%b);}}
    static long gcd(long a,long b){if(b==0l)return a;else{return gcd(b,a%b);}}
    static long lcm(long a,long b){return (a*b/gcd(a,b));}
    static long exgcd(long a,long b){if(b==0){x0=1;y0=0;return a;}long temp=exgcd(b,a%b);long t=x0;x0=y0;y0=t-a/b*y0;return temp;}
    static long pow(long a,long b){long res=1;while(b>0){if((b&1)==1)res=res*a;b>>=1;a=a*a;}return res;}
    static long mpow(long a,long b, long m){long res=1;while(b>0){if((b&1)==1)res=((res%m)*(a%m))%m;b>>=1;a=((a%m)*(a%m))%m;}return res;}
    static long mul(long a , long b){return ((a%mod)*(b%mod)%mod);}
    static long adp(long a , long b){return ((a%mod)+(b%mod)%mod);}
    static boolean isPrime(long n){if(n<=1)return false;if(n<=3)return true;if(n%2==0||n%3==0)return false;for(long i=5;i*i<=n;i=i+6)if(n%i==0||n%(i+2)==0)return false;return true;}
    static boolean isPrime(int n){if(n<=1)return false;if(n<=3)return true;if(n%2==0||n%3==0)return false;for(int i=5;i*i<=n;i=i+6)if(n%i==0||n%(i+2)==0)return false;return true;}
    static HashSet<Long> factors(long n){HashSet<Long> hs=new HashSet<Long>();for(long i=1;i<=(long)Math.sqrt(n);i++){if(n%i==0){hs.add(i);hs.add(n/i);}}return hs;}
    static HashSet<Integer> factors(int n){HashSet<Integer> hs=new HashSet<Integer>();for(int i=1;i<=(int)Math.sqrt(n);i++){if(n%i==0){hs.add(i);hs.add(n/i);}}return hs;}
    static HashSet<Long> pf(long n){HashSet<Long> ff=factors(n);HashSet<Long> ans=new HashSet<Long>();for(Long i:ff)if(isPrime(i))ans.add(i);return ans;}
    static HashSet<Integer> pf(int n){HashSet<Integer> ff=factors(n);HashSet<Integer> ans=new HashSet<Integer>();for(Integer i:ff)if(isPrime(i))ans.add(i);return ans;}
    static int[] inpint(int n){int arr[]=new int[n+1];for(int i=1;i<=n;++i){arr[i]=f.ni();}return arr;}
    static long[] inplong(int n){long arr[] = new long[n+1];for(int i=1;i<=n;++i){arr[i]=f.nl();}return arr;}
    static boolean ise(int x){return ((x&1)==0);}static boolean ise(long x){return ((x&1)==0);}
    static int gnv(char c){return Character.getNumericValue(c);}
    static int log(long x){return x==1?0:(1+log(x/2));} static int log(int x){return x==1?0:(1+log(x/2));}
    static void sort(int[] a){ArrayList<Integer> l=new ArrayList<>();for(int i:a)l.add(i);Collections.sort(l);for(int i=0;i<a.length;++i)a[i]=l.get(i);}
    static void sort(long[] a){ArrayList<Long> l=new ArrayList<>();for(long i:a)l.add(i);Collections.sort(l);for(int i=0;i<a.length;++i)a[i]=l.get(i);}
    static void sort(ArrayList<Integer> a){Collections.sort(a);}
}