program sample
    implicit none
    character(100)::s
    integer(8) :: i,j,m,n,a,b
    integer(8),allocatable :: x(:),y(:)
  
    read(*,*) s
    allocate(x(26))
    n=len_trim(s)
    x(:)=0
    do i=1,n
        a=ichar(s(i:i))-96
        x(a)=x(a)+1
    end do
    if(maxval(x)>1)then
        write(*,*)'no'
    else
        write(*,*)'yes'
    end if
  
    stop
end program sample
  

