a,b,c,y=0,-100000,1000000,[]
for i in range(int(input())):
  y=map(int,input().split())
  print(y)
  if y[0]>b and y[1]==0:
    b=y[0]
  if y[0]<c and y[1]==0:
    c=y[0]
  if abs(y[1])>a:
    a=y[1]
print(abs(b-c)*0.5*a)