import java.util.*;
import java.lang.*;
import java.io.*;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner in = new Scanner(System.in);
		int m,n,f,l; 
		boolean p=true;
		n=in.nextInt();
		m=in.nextInt();
		int[] a = new int[n];
		for (int i=0; i<m; i++){
			f=in.nextInt();
			l=in.nextInt();
			a[f-1]++; a[l-1]++;
		}
		for (int i=0; i<n; i++){if (a[i]!=a[0]){p=false; break;}}
		if (p) System.out.println("YES");
		else System.out.println("NO");
	}
}

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MyAzCjEgMgoxIDMKMiAz

3 3
1 2
1 3
2 3