#include<stdio.h>
int main(){
  int a,b,c,d;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  while(a>0||c>0){
    c=c-b;
    a=a-d;
  }
  if(a<=0){
    printf("No\n");
  }else if(c<=0){
    printf("Yes\n");
  }
}