#include<stdio.h>
#include<stdlib.h>
#define BUFSIZE 1000000
int A,B,C,D;
int rem,rem2;
int cal(int c,int d){
	if(c%d==0){
		rem2=c/d;
	}else{
		rem2=(c-c%d)/d+1;
	}
	return 0;
	
}

int main(void){
	scanf("%d %d %d %d",&A,&B,&C,&D);
	cal(C,B);
	rem=rem2;
	cal(A,D);
		
	if(rem <= rem2){
		printf("Yes");
		
	}else{
		printf("No");
	}
}