a,b,c,d = gets.chomp.split(" ").map(&:to_i)

if (a >= 0) && (c >= 0)
  puts (b*d)
elsif (b <= 0) && (d <= 0)
  puts (a*c)
elsif (b <= 0) && (c >= 0)
  puts (b*c)
elsif (d <= 0) && (a >= 0)
  puts (a*d)
elsif (b<=0) && (c<=0) && (d >=0 )
  puts (a*c)
elsif (d<= 0) && (a<=0) && (b>=0)
  puts (a*c)
elsif (c>=0) && (b>=0) && (a<= 0)
  puts (b*d)
elsif (a>=0) && (d>=0) && (c<=0)
  puts (b*d)
elsif (a<=0) && (c<=0) && (b>=0) && (d>=0)
  x = a*c
  y = b*d
  if x >= y
    puts x
  else
    puts y
  end
end
