/*No.512 魔法少女の追いかけっこ*/
import java.io.*;
import java.math.*;
import java.util.*;
public class No512 {
	public static ArrayList<BigDecimal> prepare(String a){
		String []H_a =a.split(" ");
		ArrayList<BigDecimal> al = new ArrayList<BigDecimal>(); 
		for(int i=0;i<H_a.length;i++){
			al.add(new BigDecimal(H_a[i]));
		}
		return al;
	}
	public static void main(String[] args) {
		try(BufferedReader input =new BufferedReader(new InputStreamReader(System.in))){
			ArrayList<BigDecimal> Speed = No512.prepare(input.readLine());
			ArrayList<BigDecimal> Distance = No512.prepare(input.readLine());
			boolean chase=true;
			for(int i=0;i<Distance.size()-1;i++){
				BigDecimal rapTime=Distance.get(i).divide(Speed.get(0),6,RoundingMode.DOWN);
				BigDecimal rapPoint=Speed.get(1).multiply(rapTime).setScale(2, RoundingMode.DOWN);
				if(rapPoint.compareTo(Distance.get(i+1))==1){
					chase=false;
					break;
				}
			}
			if(chase){
				System.out.println("YES");
			}else{
				System.out.println("NO");
			}			
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}