#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;
	if(A <= 0)
		break;
  }while(A == 0);

  if(C<=A)
	  printf("Yes");
  else
	  printf("No");

  return 0;
}
