import java.util.Scanner;

public class N512
{
	public static void main(String[] args)
	{
		Scanner sc =new Scanner (System.in);
		double X=sc.nextInt();
		double Y=sc.nextInt();
		int N=sc.nextInt();
		int[] A=new int[N];
		int buf=0;
		for(int i=0;i<N;i++)
		{
			A[i]=sc.nextInt();
		}
		double xtime=0;
		double now=0;
		double next=0;
		String msg="YES";
		String emsg="";
		for(int i=0;i<N-1;i++)
		{
			now=A[i];
			next=A[i+1];
			xtime=now/X;
			//System.out.print(xtime*Y+"　");
			if(xtime*Y>=next+0.1)
			{
				msg="NO";
				//emsg="now:"+now+"next"+next+"Y:"+(xtime*Y);
			}
		}
		//System.out.println("");
		//System.out.println(emsg);
		System.out.println(msg);
	}
}