integer::N,i,kankaku,tmp
  integer,allocatable::x(:),memo(:)
  integer::min1,min2
  read *, N
  allocate(x(N),memo(0: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
  memo(1:2) = 0

  do i=3,N
     memo(i) = 0
     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

  do i=1,N-1
     if(MOD((x(i)-min1),kankaku).ne.0) then
        print '(a)', "NO"
        return
     end if
     tmp = (x(i)-min1)/kankaku
     if(memo(tmp).eq.1) then
        print '(a)', "NO"
        return
     end if
     memo(tmp) = 1
  end do

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