X,Y = gets.split.map(&:to_i)
N = gets.to_i
A = gets.split.map(&:to_i)
S = Array.new(N + 1, 0)
A.each_with_index do |a,i|
  S[i + 1] = S[i] + a
end
ans = (1 ... N).none? do |i| 
  Y * S[i] >  S[i + 1] * X
end
puts ans ? "YES" : "NO"