s="gets.split.map{|e| e.to_f}"
a,b=eval s
n=gets.to_i
x=eval s
a=a*1000/3600
b=b*1000/3600

ok="YES"
(n-1).times{|i|
	t=x[i]/a
	ok="NO" if x[i+1]<t*b
}
puts ok