#include <stdio.h>

int main(void){

  int A, B, C, D;

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

  do{
	  C=C-B;
	  if(C<=0)
		  break;
	  A=A-D;
  }while(A<=0);

  if(C>=0)
	  printf("Yes");
  else
	  printf("No");

  return 0;
}
