n=int(input())
l=sorted(list(map(int, input().split())))
X=0
for i in range(n-1):
    x=l[i]-l[i+1]
    if i==0:
        X=x
        continue
    if x!=X or l[i]==l[i+1]:
        print("NO")
        break
    X=x
else:
    print("YES")