import sys

def get_jiaoji(q_1, q_2):
    j_ = []
    if(q_1[1] >= q_2[0] and q_1[0] <= q_2[0] ):
        j_ = [q_2[0], min(q_1[1], q_2[1])]
    elif(q_2[1] >= q_1[0] and q_2[0] <= q_1[0]):
        j_ = [q_1[0], min(q_2[1], q_1[1])]
    else:
        j_ = [-10E-9, -10E-9]
    return j_
    
    
    
for line in sys.stdin:
    a = line.split()
    qujian_1 = [int(a[0]), int(a[1])]
    qujian_2 = [int(a[2]), int(a[3])]
    qujian_3 = [int(a[4]), int(a[5])]
    max_ans = -1000
    jiaoji_1 = get_jiaoji(qujian_1, qujian_2)
    jiaoji_2 = get_jiaoji(qujian_2, qujian_3)
    jiaoji_3 = get_jiaoji(qujian_1, qujian_3)
    ans = 2 * max(jiaoji_1[-1], jiaoji_2[-1], jiaoji_3[-1])
    if (ans < 0):
        ans = -1
    print(ans)