#include<stdio.h>

int main(void)
{
   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");

   return 0;
}
