Problem:
Score : 500 points

Problem Statement

Takahashi is not good at problems about trees in programming contests, and Aoki is helping him practice.

First, Takahashi created a tree with N vertices numbered 1 through N, and wrote 0 at each edge.

Then, Aoki gave him M queries. The i-th of them is as follows:

Increment the number written at each edge along the path connecting vertices a_i and b_i, by one.

After Takahashi executed all of the queries, he told Aoki that, for every edge, the written number became an even number.
However, Aoki forgot to confirm that the graph Takahashi created was actually a tree, and it is possible that Takahashi made a mistake in creating a tree or executing queries.

Determine whether there exists a tree that has the property mentioned by Takahashi.

Constraints

2 ≤ N ≤ 10^5

1 ≤ M ≤ 10^5

1 ≤ a_i,b_i ≤ N

a_i ≠ b_i

Input

Input is given from Standard Input in the following format:

N M
a_1 b_1
:
a_M b_M

Output

Print YES if there exists a tree that has the property mentioned by Takahashi; print NO otherwise.

Sample Input 1

4 4
1 2
2 4
1 3
3 4

Sample Output 1

YES

For example, Takahashi's graph has the property mentioned by him if it has the following edges: 1-2, 1-3 and 1-4.
In this case, the number written at every edge will become 2.

Sample Input 2

5 5
1 2
3 5
5 1
3 4
2 3

Sample Output 2

NO

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Runtime Error)

//繰り返し二乗法 repow(b,p)(b,p,modder)
//ユークリッド互除法で最大公約数 gcd
//gcdで最小公倍数 lcm
//約数列挙divList(int)
//BSA()()()(List<T>,T,int,int,Comparator<T>)
//BSF()()()(List<T>,T,int,int,Comparator<T>)
//BSL()()()(List<T>,T,int,int,Comparator<T>)
//文字列文字ソートStSort(String)
//二次元整数座標オブジェクトXy
////toString
////偏角ソート用hencom
////偏角henkaku
////equals
//スキャナーScnr
////next nextBuilder nextInt nextLong nextDouble()
////nextAint nextAlong nextAdouble(n)(a[],n)
//static PrintWriter out = new PrintWriter(System.out);
import java.util.*;
import java.io.*;

class Main{
  static int repow(int b,int p){
    long a = b;
    long res=1;
    while(p>0){
      if(p%2==1){
        res*=a;
      }
      a*=a;
      p/=2;
    }
    return (int)res;
  }
  static int repow(int b,int p,int modder){
    long a = b%modder;
    long res=1;
    while(p>0){
      if(p%2==1){
        res=(res*a)%modder;
      }
      a=(a*a)%modder;
      p/=2;
    }
    return (int)res;
  }
  static <T extends Number> long gcd(T cc,T dd){
    long c=cc.longValue();
    long d=dd.longValue();
    while(true){
      long f=c%d;
      if(f==0){
        return d;
      }
      c=d;
      d=f;   
    }
  }
  static <T extends Number> long lcm(T cc,T dd){
    long c=cc.longValue();
    long d=dd.longValue();
    return c/gcd(c,d)*d;
  }
  static ArrayList<Integer> divList(int n){
    ArrayList<Integer> div=new ArrayList<Integer>();
    for(int i=1;i*i<=n;i++){
      if(n%i==0){
        div.add(i);
        div.add((int)(n/i));
      }
    }
    return div;
  }
  static <T extends Comparable> int BSA(List<T> l,T target){
    return BSA(l,target,0,l.size(),(s1,s2)->s1.compareTo(s2));
  }
  static <T> int BSA(List<T> l,T target,Comparator<T> c){
    return BSA(l,target,0,l.size(),c);
  }
  static <T extends Comparable> int BSA(List<T> l,T target,int left,int right){
    return BSA(l,target,left,right,(s1,s2)->s1.compareTo(s2));
  }
  static <T> int BSA(List<T> l,T target,int left,int right,Comparator<T> c){
    int lt = left;
    int rt = right-1;
    while(lt<=rt){
      T gaze=l.get(lt+(rt-lt)/2);
      if(c.compare(gaze,target)<0){
        lt=lt+(rt-lt)/2+1;
      }else if(c.compare(gaze,target)>0){
        rt=lt+(rt-lt)/2-1;
      }else{
        return lt+(rt-lt)/2;
      }
    }
    return -1;
  }
  static <T extends Comparable> int BSF(List<T> l,T target){
    return BSF(l,target,0,l.size(),(s1,s2)->s1.compareTo(s2));
  }
  static <T> int BSF(List<T> l,T target,Comparator<T> c){
    return BSF(l,target,0,l.size(),c);
  }
  static <T extends Comparable> int BSF(List<T> l,T target,int left,int right){
    return BSF(l,target,left,right,(s1,s2)->s1.compareTo(s2));
  }
  static <T> int BSF(List<T> l,T target,int left,int right,Comparator<T> c){
    int lt = left;
    int rt = right-1;
    while(lt<=rt){
      T gaze=l.get(lt+(rt-lt)/2);
      if(c.compare(gaze,target)<0){
        lt=lt+(rt-lt)/2+1;
      }else if(c.compare(gaze,target)>=0){
        rt=lt+(rt-lt)/2-1;
      }
    }
    return lt;
  }
  static <T extends Comparable> int BSL(List<T> l,T target){
    return BSL(l,target,0,l.size(),(s1,s2)->s1.compareTo(s2));
  }
  static <T> int BSL(List<T> l,T target,Comparator<T> c){
    return BSL(l,target,0,l.size(),c);
  }
  static <T extends Comparable> int BSL(List<T> l,T target,int left,int right){
    return BSL(l,target,left,right,(s1,s2)->s1.compareTo(s2));
  }
  static <T> int BSL(List<T> l,T target,int left,int right,Comparator<T> c){
    int lt = left;
    int rt = right-1;
    while(lt<=rt){
      T gaze=l.get(lt+(rt-lt)/2);
      if(c.compare(gaze,target)<=0){
        lt=lt+(rt-lt)/2+1;
      }else if(c.compare(gaze,target)>0){
        rt=lt+(rt-lt)/2-1;
      }
    }
    return lt;
  }
  static String StSort(String s){
    StringBuilder sb = new StringBuilder(s);
    int lg = sb.length();
    int l;
    int r;
    int gaze;
    for(int i=1;i<lg;i++){
      l=0;
      r=i-1;
      while(l<=r){
        gaze=(l+r)/2;
        if(sb.charAt(gaze)<=sb.charAt(i)){
          l=gaze+1;
        }else if(sb.charAt(gaze)>sb.charAt(i)){
          r=gaze-1;
        }
      }
      sb.insert(l,sb.charAt(i));
      sb.deleteCharAt(i+1);
    }
    return sb.toString();
  }
  static class Xy{
    int x;
    int y;
    Xy(int x,int y){
      this.x=x;
      this.y=y;
    }
    public String toString(){
      return "["+x+","+y+"]";
    }
    public double henkaku(){
      return Math.atan2(y,x);
    }
    public static int hencom(Xy s1,Xy s2){
      return (int)Math.signum(s1.henkaku()-s2.henkaku());
    }
    public boolean equals(Object o){
      return x==((Xy)o).x&&y==((Xy)o).y;
    }
  }
  static class Scnr{
    private final InputStream ins;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    Scnr(){
      this(System.in);
    }
    Scnr(InputStream in){
      ins = in;
    }
    private boolean hasNextByte(){
      if(ptr<buflen){
        return true;
      }else{
        ptr = 0;
        try{
          buflen = ins.read(buffer);
        }catch(IOException e){
          e.printStackTrace();
        }
        if(buflen<=0){
          return false;
        }
      }
      return true;
    }
    private int readByte(){
      if(hasNextByte()){
        return buffer[ptr++];
      }else{
        return -1;
      }
    }
    private static boolean isPrintableChar(int c){
      return 33<=c&&c<=126;
    }
    public boolean hasNext(){
      while(hasNextByte()&&!isPrintableChar(buffer[ptr])){
        ptr++;
      }
      return hasNextByte();
    }
    public String next(){
      if(!hasNext()){
        throw new NoSuchElementException();
      }
      StringBuilder sb = new StringBuilder();
      int b = readByte();
      while(isPrintableChar(b)){
        sb.appendCodePoint(b);
        b = readByte();
      }
      return sb.toString();
    }
    public StringBuilder nextBuilder(){
      if(!hasNext()){
        throw new NoSuchElementException();
      }
      StringBuilder sb = new StringBuilder();
      int b = readByte();
      while(isPrintableChar(b)){
        sb.appendCodePoint(b);
        b = readByte();
      }
      return sb;
    }
    public double nextDouble(){
      return Double.parseDouble(next());
    }
    public long nextLong(){
      if(!hasNext()){
        throw new NoSuchElementException();
      }
      long n = 0;
      boolean minus = false;
      int b = readByte();
      if(b=='-'){
        minus=true;
        b=readByte();
      }
      if(b<'0'||'9'<b){
        throw new NumberFormatException();
      }
      while(true){
        if('0'<=b&&b<='9'){
          n*=10;
          n+=b-'0';
        }else if(b==-1||!isPrintableChar(b)){
          return minus?-n:n;
        }else{
          throw new NumberFormatException();
        }
        b=readByte();
      }
    }
    public int nextInt(){
      long nl=nextLong();
      if(nl<Integer.MIN_VALUE||Integer.MAX_VALUE<nl){
        throw new NumberFormatException();
      }
      return (int) nl;
    }
    public int[] nextAInt(int n){
      int[] a = new int[n];
      nextAInt(a,n);
      return a;
    }
    public void nextAInt(int[] a,int n){
      for(int i=0;i<n;i++){
        a[i] = nextInt();
      }
    }
    public long[] nextALong(int n){
      long[] a = new long[n];
      nextALong(a,n);
      return a;
    }
    public void nextALong(long[] a,int n){
      for(int i=0;i<n;i++){
        a[i] = nextLong();
      }
    }
    public double[] nextADouble(int n){
      double[] a = new double[n];
      for(int i=0;i<n;i++){
        a[i] = nextDouble();
      }
      return a;
    }
    public void nextADouble(double[] a,int n){
      for(int i=0;i<n;i++){
        a[i] = nextDouble();
      }
    }
  }
  
  static Scnr sc = new Scnr();
  static PrintWriter out = new PrintWriter(System.out);
  public static void main(String args[]){
    int n = sc.nextInt();
    int m = sc.nextInt();
    boolean[] a = new boolean[n];
    Arrays.fill(a,false);
    for(int i=0;i<n;i++){
      int d=sc.nextInt()-1;
      a[d]=!a[d];
      d=sc.nextInt()-1;
      a[d]=!a[d];
    }
    for(int i=0;i<n;i++){
      if(a[i]){
        out.println("NO");
        out.flush();
        return;
      }
    }
    out.println("YES");
    out.flush();
  }
}