#include<stdio.h>
int main()
{
	int a,b,c,d;
	scanf("%d %d %d %d", &a,&b,&c,&d);

	while(1){
      a=a-d;
      c=c-b;
      if(a<=0)
		printf("No\n");
      break;
      if(b<=0)
        printf("Yes\n");
      break;

	}
 
	return 0;
}
