#include <stdio.h>
int main(void){
  int t_attack,t_hp;
  int a_attack,a_hp;
  scanf("%d%d%d%d",&t_hp,&t_attack,&a_hp,&a_attack);
  while(1){
    a_hp=a_hp - t_attack;
    if(a_hp<=0)break;
    t_hp=t_hp - a_attack;
    if(t_hp<=0)break;
  }
  if(a_hp<=0)printf("Yes");
  if(t_hp<=0)printf("No");
  return 0;
}
