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)