n = int(input())
x = list(map(int, input().strip().split(' ')))
x.sort()
h = []
for (u, v) in zip(x[0:n-1], x[1:n]):
    h.append(v - u)
h.sort()
if h[0] > 0 and h[0] == h[len(h) - 1]:
    print('YES')
else:
    print('NO')