#include<stdio.h>

int main(void){
  int tH, tA, aH, aA,Tw,Aw;
  scanf("%d %d %d %d",&tH, &tA, &aH, &aA);
  	
  /*(A / D)回目攻撃のときAのHPが0以下＝Tの(B / C)回目の攻撃のとき*/
  Tw = (tH + aA - 1) / aA; 
  Aw = (aH + tA - 1) / tA; 
  
  if(Tw >= Aw)
    printf("Yes\n");
  else
    printf("No\n");
  return 0;
}