N = int(input())
ans = True
S = list(map(int, input().split()))
S.sort()
d = S[1] - S[0]
for i in range(1, N - 1):
    if d != S[i + 1] - S[i]:
        ans = False
        break
if ans and d != 0:
    print("YES")
else:
    print("NO")