x_speed, y_speed = gets.split.map(&:to_i)
count = gets.chomp.to_i
list = gets.split.map(&:to_i)
flag = true
(count - 1).times do |i|
	if list[i] * y_speed > list[i + 1] * x_speed
		break flag = false
	end
end
puts flag ? "YES" : "NO"