import java.util.*;
import java.io.*;
public class Main {
        static public class InputIterator{
          ArrayList<String> inputLine = new ArrayList<String>(1024);
          int index = 0;
          int max;
          InputIterator(){
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            while(true){
              String read;
              try{
                read = br.readLine();
              }catch(IOException e){
                read = null;
              }
              if(read != null){
                inputLine.add(read);
              }else{
                break;
              }
            }
            max = inputLine.size();
          }
          public boolean hasNext(){return (index < max);}
          public String next(){
            if(hasNext()){
              String returnStr = inputLine.get(index);
              index++;
              return returnStr;
            }else{
              throw new IndexOutOfBoundsException("これ以上入力はないよ。");
            }
          }
        }
        
        static InputIterator ii = new InputIterator(); 
        static void myout(Object t){System.out.println(t);}//standard output
        static void myerr(Object t){System.err.println(t);}//standard error
        static String next(){return ii.next();}
        static int nextInt(){return Integer.parseInt(next());}
        static long nextLong(){return Long.parseLong(next());}
        static String[] nextStrArray(){return next().split(" ");}
        static ArrayList<Integer> nextIntArray(){
          ArrayList<Integer> ret = new ArrayList<Integer>();
          String[] input = nextStrArray();
          for(int i = 0; i < input.length; i++){
            ret.add(Integer.parseInt(input[i]));
          }
          return ret;
        }
        static ArrayList<Long> nextLongArray(){
          ArrayList<Long> ret = new ArrayList<Long>();
          String[] input = nextStrArray();
          for(int i = 0; i < input.length; i++){
            ret.add(Long.parseLong(input[i]));
          }
          return ret;
        }
        static char[] nextCharArray(){return mySplit(next());}
        static char[] mySplit(String str){return str.toCharArray();}
        static String kaigyoToStr(String[] list){return String.join("\n",list);}
        static String kaigyoToStr(ArrayList<String> list){return String.join("\n",list);}
        static String hanSpToStr(String[] list){return String.join(" ",list);}
        static String hanSpToStr(ArrayList<String> list){return String.join(" ",list);}
        public static void main(String[] args){
          ArrayList<Long> tmp = nextLongArray();
          long L = tmp.get(0);
          long R = tmp.get(1);
          long M = tmp.get(2);
          long K = tmp.get(3);
          long maxL = L * K;
          long maxR = R * K;
          if(maxR - maxL >= M){
            myout("Yes");
          }else{
            maxL %= M;
            maxR %= M;
            if(maxL >= maxR){
              myout("Yes");
            }else{
              myout("No");
            }
          }
          
        }
        //Method addition frame start

        //Method addition frame end
}