#include<stdio.h>
int main(){
  int A,B,C,D;
  scanf("%d %d %d %d",&A ,&B ,&C ,&D);
  do{
    C=C-B;
    A=A-D;
  }while((C>0)&&(A>0));
  if(C<=0){
    printf("Yes");
  }
  else{
   	printf("No");
  }
  return 0;
}