#include<stdio.h>
 
int main(void){
  
  int hp1,hp2,atk1,atk2;
  scanf("%d %d %d %d",&hp1,&hp2,&atk1,&atk2);
  int cnt=0;
  
  while(hp1>0 && hp2>0){
    if(cnt%2==0){
      hp2-=atk1;
    }else{
      hp1-=atk2;
    }
    cnt++;
  }
  
  if(hp1<=0){
    printf("No");
  }else{
    printf("Yes");
  }
  
  return 0;
}