s=input()
s=s.split(' ')
maxx=0
if int(s[0])*int(s[1])+int(s[2])*int(s[3])>maxx:
    maxx=int(s[0])*int(s[1])+int(s[2])*int(s[3])
if int(s[0])*int(s[2])+int(s[1])*int(s[3])>maxx:
    maxx=int(s[0])*int(s[2])+int(s[1])*int(s[3])
if int(s[0])*int(s[3])+int(s[1])*int(s[2])>maxx:
    maxx=int(s[0])*int(s[3])+int(s[1])*int(s[2])
print(maxx)