import java.util.Scanner;

public class b {
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int foo[] = new int[N];
		for(int i = 0; i < N; i++)
			foo[i] = sc.nextInt();
		int min = 114514810;
		int min2th = 364364893;
		for(int i = 1; i < N; i++){
			if(foo[i] < min){
				min2th = min;
				min = foo[i];
			}else if(foo[i] < min2th){
				min2th = foo[i];
			}
			if(foo[i] < foo[i - 1]){
				int tmp = foo[i];
				foo[i] = foo[i - 1];
				foo[i - 1] = tmp;
			}else if(foo[i] == foo[i - 1]){
				System.out.println("NO");
				return;
			}
		}
		int bar = min2th - min;
		if(bar == 0){
			System.out.println("NO");
			return;
		}
		for(int i = 0; i < N - 1; i++){
			if(foo[i] + bar != foo[i + 1]){
				System.out.println("NO");
				return;
			}
		}
		System.out.println("YES");
	}
}