program sumitrust2019b
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: n,i

    read*, n
    do i=1,n
        if (int(i*1.08d0) == n) then
            print'(i0)', i
            stop
        end if
    end do
    print'(a)', ':('
end program sumitrust2019b