#include<stdio.h>
#include<math.h>

int main(void){

  int th,ta,ah,aa;

  scanf("%d %d %d %d",&th,&ta,&ah,&aa);

  while(ah>0 && th>0){
    ah=ah-ta;
    th=th-aa;
  }
  if(ah<=0)printf("Yes");
  else if(th<=0)printf("No");
  return 0;
}