x, y = gets.chomp.split.map(&:to_i)
n = gets.to_i
as = [0] + gets.chomp.split.map(&:to_i) + [10000000000]

ok = true
(1...as.size - 1).each do |i|
  if as[i - 1] * y <= as[i] * x and as[i] * x <= as[i + 1] * y
    :ok
  else
    ok = false
  end
  break unless ok
end

if ok
  puts :YES
else
  puts :NO
end