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