n = int(input())
A = sorted(list(map(int,input().split())))
if len(set(A))!=n:
    print('NO')
else:
    dis = A[1]-A[0]
    flg = True
    for i in range(1, n):
        if A[i] - A[i-1] != dis:
            flg = False
            break
    print('YES' if flg else 'NO')