#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int main(void){
  int thp,tak,ahp,aak;
  (void)scanf("%d %d %d %d",&thp,&tak,&ahp,&aak);
  while(thp>0){
    ahp-=tak;
    if(ahp<=0){
      printf("Yes\n");
      break;
    }
    thp-=aak;
  }
  if(thp<=0)printf("No\n");
  return 0;
}