# yukicoder No.406 鴨等間隔の法則

N = int(input())
X = [int(x) for x in input().split()]
X.sort()
ans = "YES"

for i in range(N):
    if i == 1:
        interval = X[i] - X[i - 1]

        if interval == 0:
            ans = "NO"
            break
    elif i > 1:
        if X[i] - X[i - 1] != interval:
            ans = "NO"
            break

print(ans)