program main
      implicit none
      integer :: n, cnt, i
      integer(8), allocatable :: a(:)

      read *, n
      allocate( a(n) )
      read *, a

      call quicksort1( a, 1, n )
      cnt = 0
      do i = 1, n-1
        if ( a(i) == a(i+1) ) then
        else
          cnt = cnt + 1
        end if
      end do
      if ( cnt == n - 1 ) then
        print *, 'YES'
      else
        print *, 'NO'
      end if

end program main
recursive subroutine quicksort1(a, first, last)
  implicit none
  integer(8),intent(inout)::a(*)
  integer,intent(in)::first,last
  !
  ! Original
  ! https://gist.github.com/t-nissie/479f0f16966925fa29ea
  !
  integer(8)::x,t
  integer::i,j

  x = a((first+last)/2)
  i = first
  j = last
  do
     do while (a(i) < x)
        i=i+1
     end do
     do while (x < a(j))
        j=j-1
     end do
     if (i >= j) exit
     t = a(i)
     a(i) = a(j)
     a(j) = t
     i=i+1
     j=j-1
  end do
  if (first < i-1) call quicksort1(a, first, i-1)
  if (j+1 < last)  call quicksort1(a, j+1, last)

  return
end subroutine quicksort1
