#include<stdio.h>
int main(void){
  int a,b,c,d,i,e,f;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  for(i=1;i<=100;i++){
    a=a-d;
    c=c-b;
    /*printf("%d %d\n",a,c);*/
    if(c<=0){
      printf("Yes\n");
        break;
    }else if(a<=0){
      printf("No\n");
        break;
    }
  }
  return 0;
}
