import java.util.Arrays;
import java.util.Scanner;
public class Main{
	public static void main(String[] args){
		solver();
	}
	static void solver(){
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		long[] x=new long[n];
		for(int i=0;i<n;i++){
			x[i]=sc.nextInt();
		}
		Arrays.sort(x);
		long d=x[1]-x[0];
		if(d==0){
			System.out.println("NO");
			return;
		}
		for(int i=0;i<n-1;i++){
			if(x[i+1]-x[i]!=d){
				System.out.println("NO");
				return;
			}
		}
		System.out.println("YES");
	}
}