#include<stdio.h>

int main(){
   int A,B,C,D;
   int x;
   int y;
   scanf("%d %d %d %d",&A,&B,&C,&D);
   x=(C+B-1)/B;
   y=(A+D-1)/D;
   if(x<=y){
      printf("Yes");
   }
   if(x>y){
      printf("No");
   }
   return 0;
}
