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

x = 0
y = 0
if a >= b && a > 0
  x = a
elsif a >= b && a < 0
  x = a
elsif a <= b && b > 0
  x = b
elsif a <= b && b < 0
  x = b
end

if x < 0 && c <= d
  y = c
elsif x < 0 && c >= d
  y = d 
elsif x > 0 && c <= d
  y = d
elsif x > 0 && c >= d
  y =c
end
puts x*y