#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 -=b;
      if(c<=0){
         printf("Yes");
         break;
      }
      a -=d;
      if(a<=0){
         printf("No");
         break;
      }
   }
   
   return 0;
}
