X, Y = gets.split.map(&:to_i)
N = gets.to_i
a = gets.split.map(&:to_i)
y_x_ratio = Y / X

overtaking_point = 0.upto(N - 2).find { |i|
  a[i] * y_x_ratio > a[i + 1]
}

puts overtaking_point.nil? ? 'YES' : 'NO'