#include<stdio.h>
int main(void){
	int A,B,C,D,x=0,y=0;
	scanf("%d %d %d %d",&A,&B,&C,&D);
	while(C>0){
		C=C-B;
		x=x+1;
	}
	while(A>0){
		A=A-D;
		y=y+1;
	}
	if(x>y){
		printf("No\n");
	}
	if(x<=y){
		printf("Yes\n");
	}
	return 0;
}