#include<stdio.h>
int main(){
  int a,b,c,d;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  while(b>0&&d>0){
    d=d-a;
    b=b-c;
  }
  if(b<=0){
    printf("No\n");
  }else if(d<=0){
    printf("Yes\n");
  }
}