program kadai
integer  ::  N,i
integer,allocatable  ::  A(:)


read(*,*) N
allocate(A(N))
read(*,*) A

call qsort(A)
do i=1,N-1
    if(A(i)==A(i+1)) then
        write(*,*) "NO"
        stop
    end if
end do
write(*,*) "YES"
stop

contains
!入れ替え!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
subroutine swap(a,b)
implicit none
integer,intent(inout)  ::  a,b
integer  ::  c
c=a
a=b
b=c
end subroutine swap

subroutine qsort(x)
implicit none
integer, intent(inout)  ::  x(:)
integer  ::  first,last
first=1
last=size(x)
call q2sort(x,first,last)
return
end subroutine qsort

recursive subroutine q2sort(x,first,last)
implicit none
integer, intent(inout)  ::  x(:)
integer, intent(inout) ::  first,last
integer  ::  fir, las
integer  ::  i,j
integer  ::  n
n=x((first+last)/2)
i=first
j=last
do
do while (x(i)<n)
i=i+1
end do
do while(x(j)>n)
j=j-1
end do
if (i>j .or. i==j) then
exit
end if
call swap(x(i),x(j))
i=i+1
j=j-1
end do
if (first<i-1) then
las=i-1
call q2sort(x,first,las)
end if
if (last>j+1) then
fir=j+1
call q2sort(x,fir,last)
end if
end subroutine q2sort
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


end program kadai
