program main
  implicit none
  integer::N,i,kankaku,tmp
  integer,allocatable::x(:)
  integer::memo(0:10**8)
  integer::min1,min2
  data memo/100000001*0/
  read *, N
  allocate(x(N))
  read *, x

  min1 = MIN(x(1),x(2))
  min2 = MAX(x(1),x(2))
  if(min1.eq.min2) then
     print '(a)', "NO"
     return
  end if


  do i=3,N
     memo(x(i)) = 1
     if(min1.gt.x(i)) then
        min2 = min1
        min1 = x(i)
     else if(min2.gt.x(i)) then
        min2 = x(i)
     end if
  end do

  kankaku = min2 - min1
  tmp = min1 + kankaku*2
  do i=3,N-1
     if(memo(tmp).ne.0) then
        print '(a)', "NO"
        return
     end if
  end do

  print '(a)', "YES"
end program