program main
  implicit none
  integer::X,Y,N,i
  integer,allocatable::a(:)
  read *,X,Y
  read *,N
  allocate(a(N))
  read *,a
  do i=2,N
     if(a(i)*X.ge.a(i-1)*y) then
        continue
     else
        print '(a)',"NO"
        return
     end if
  end do
  print '(a)',"YES"
end program main