n = int(input())
l = sorted(map(int, input().split()))

l2 = []
for i in range(n-1):
    l2.append(l[i+1] - l[i])

if len(set(l2)) > 1:
    print('NO')
elif len(set(l2)) == 1 and set(l2) == {0}:
    print('NO')
else:
    print('YES')