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


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

if 0 in l2:
    print('NO')

else:
    if len(set(l2)) != 1:
        print('NO')
    else:
        print('YES')