#include<stdio.h>

int main(){
   int a,b,c,d;

   scanf("%d %d %d %d", &a, &b, &c, &d);

   int x = (a+d-1)/d;
   int y = (c+b-1)/b;

   if(x >= y){
      printf("Yes\n");
   }else{
      printf("No\n");
   }
   return 0;
}