a = input()
b = input()
c = input()
d = input()

s1 = a*b + c*d
s2 = a*c + b*d
s3 = a*d + b*c

if (s1>s2) and (s1>s3):
    print(s1)
if (s2>s1) and (s2>s3):
    print(s2)
if (s3>s1) and (s3>s2):
    print(s3)