function f(x, y)
      f = 1/(x+y)
      end

      program main
      common /values/ x1, x2, y1, y2, hx, hy

      call input
      call output
      write (*,*) 'OK'

      pause
      end

      subroutine input
      character*20 msg
      common /values/ x1, x2, y1, y2, hx, hy
      open(1, file = 'input.txt')
      read(1,*) x1, x2, hx
      read(1,*) y1, y2, hy

      if (((x2-x1).GT.0.AND.hx.LT.0).OR.((x2-x1).LT.0.AND.hx.GT.0)) then
      msg = 'invalid input data for x'
      call exeption(msg)
      end if
      if (((y2-y1).GT.0.AND.hy.LT.0).OR.((y2-y1).LT.0.AND.hy.GT.0)) then
      msg = 'invalid input data for y'
      call exeption(msg)
      end if
      end

      subroutine output
      logical bm, bn
      common /values/ x1, x2, y1, y2, hx, hy

 100  format (E10.4, '   ' \)
 101  format (A11, '    ' \)
 102  format (E11.4, '    ' \)
 103  format (A10, '   ' \)
 104  format (A10)

      open(2, file = 'output.txt')

      a = abs((x2-x1)/hx)
      b = abs((y2-y1)/hy)

      m = a + 1
      n = b + 1

      bm = (a - int(a)).NE.0
      bn = (b - int(b)).NE.0

      if (bm) m = m + 1
      if (bn) n = n + 1

      write(2, 101) 'y\x'

      do x = x1,x2,hx
        write(2, 100) x
      end do

      if (bm) write(2, 100) x2

      write(2, 104)
      write(2, 104)

      do y = y1,y2,hy
        write(2, 102) y
        do x = x1,x2,hx
            if ((x+y).NE.0) then
                write(2, 100) f(x, y)
            else
                write(2, 103) '+inf'
            end if
        end do
        if (bm) write(2, 100) f(x2, y)
        write (2, 104)
      end do

      if (bn) then
        write(2, 102) y
        do x = x1,x2,hx
            if ((x+y).NE.0) then
                write(2, 100) f(x, y2)
            else
                write(2, 103) '+inf'
            end if
        end do
        if (bm) write(2, 100) f(x2, y2)
        write (2, 104)
      end if

      close(2)
      end

      subroutine exeption(message)
      character*20 message
      print *, message
      pause
      stop
      end