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