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)
"""
pass