#include<stdio.h>
#include<math.h>

int main(){

 int A,B,C,D;
 scanf("%d %d %d %d",&A,&B,&C,&D);

 int takashi = (C / B);
 if (C%B != 0){takashi += 1;} 

 int aoki = (A / D);
 if(A%D != 0){aoki += 1;}

 if(takashi>=aoki){
	printf("Yes");
}else{
	printf("No");
}



return 0;
}