program bardia
      dimension x(10000),y(10000)
      character*20 file1
      character*20 file2
      read(*,'(a20)')file1
      read(*,'(a20)')file2
      open(1,file=file1) 
      open(2,file=file2) 
c
      do 10 i=1,10000  
       read(1,*,END=11) x(i),y(i)
10    continue
11    n=i-1
      x(0)=2*x(1)-x(2)
      y(0)=y(1)
      x(n+1)=2*x(n)-x(n-1)
      y(n+1)=y(n)
      do 20 i=1,n+1
       write(2,*) (x(i)+x(i-1))/2,y(i-1)
       write(2,*) (x(i)+x(i-1))/2,y(i)
20    continue       
      close(1)
      close(2)
      end