#include<stdio.h>
int main(){
  int A,B,C,D;
  scanf("%d%d%d%d",&A,&B,&C,&D);
  
  while(1){
    C=C-B;
    if(C<=0)break;
    A=A-D;
    if(A<=0)break;
    }
 if(C<=0) printf("Yes");
  else printf("No");
    }