N = int(input())
l = list(map(int, input().split()))
l.sort()
ck = l[1] - l[0] 
ck1 = 0
flg = 0
for i in range(len(l) - 1):
    ck1 = l[i + 1] - l[i]
    if ck1 != ck:
        flg = 1
        break
    ck = ck1

if ck == 0 or flg == 1:
    print("NO")
else:
    print("YES")