#include<stdio.h>

int main(void){

  int A,B,C,D,T_attack_num,A_attack_num;

  scanf("%d %d %d %d",&A,&B,&C,&D);
  if(C % B == 0) T_attack_num = C/B;
  else T_attack_num = (C/B)+1;

  if(A % D == 0) A_attack_num = C/B;
  else A_attack_num = (C/B)+1;

  if(T_attack_num <= A_attack_num) printf("Yes\n");
  else printf("No\n");
  return 0;
}
