      PROGRAM taxRate
      IMPLICIT NONE
      integer :: n
      integer :: i,x
      
      read*,n
      
      do i = 1,n
        x = i * 108 / 100
        if( x==n ) goto 100
      end do
      
      
      print'(a)',':('
      RETURN
      
 100  continue
      print*,i
      
      
      
      
      
      END PROGRAM