#include<stdio.h>
int main(void){
  int a,b,c,d;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  int taka=a;
  int aoki=c;
  while(1){
    aoki=aoki-b;
    taka=taka-d;
    if(taka<=0 && aoki>0){
      printf("No\n");
      break;
    }else if(aoki<=0 && taka>0){
      printf("Yes\n");
      break;
    }
  }
  return 0;
}