x, y = gets.split.map {|c| c.to_i / 3600.0 * 1000.0 } # mps
_ = gets
a = gets.split.map(&:to_i)

a.each_cons(2) do |r, s|
  time = r / x
  if y * time > s + 0.00000001
    puts "NO"
    exit
  end
end

puts "YES"