import java.util.Arrays;
import java.util.Scanner;

public class N406 {

	public static void main(String[] args)
	{
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		int[] x=new int[n];
		int dif=-1;
		String ans="NO";
		for(int i=0;i<n;i++)
		{
			x[i]=sc.nextInt();
		}
		Arrays.sort(x);
		for(int i=1;i<n;i++)
		{
			int buf=x[i]-x[i-1];
			if(buf==0){break;}
			if(dif==-1){dif=buf;continue;}
			if(dif!=buf){break;}
			if(i==n-1){ans="YES";}
		}
		System.out.println(ans);
	}

}