n = int(input())
D = list(map(int, input().split()))

D.sort()
d = D[1] - D[0]
if d == 0:
    print("NO")
    exit()
for i in range(1, n - 1):
    if D[i + 1] - D[i] != d:
        print("NO")
        exit()
print("YES")