n=int(input())
*x,=map(int,input().split())

lx=set(x)
if len(lx)<len(x):
	print('NO')
else:
	x.sort()
	d=[x[i+1]-x[i] for i in range(len(x)-1)]
	print('YNEOS'[len(set(d))>1::2])