l = list(map(int, input().split(" ")))
r1 = [l[0], l[1]]
r2 = [l[2], l[3]]
r3 = [l[4], l[5]]
def qujian(x, y):
    if x[1] < y[1] and x[1] >= y[0]:
        return(2*x[1])
    if y[1] < x[1] and y[1] >= x[0]:
        return(2*y[1])
    else: return(-1)

ans1 = qujian(r1, r2)
ans2 = qujian(r2, r3)
ans3 = qujian(r3, r1)

print(max(ans1, ans2, ans3))