#include <stdio.h>
int main(void){
  int th, ta, ah, aa;
  scanf("%d %d %d %d", &th, &ta, &ah, &aa);
  int turnt, turna;
  turnt = th / aa;
  if(th % aa != 0){
    turnt++;
  }
  turna = ah / ta;
    if(ah % ta != 0){
    turna++;
  }
  if(turna > turnt){
    printf("No\n");
  }else{
    printf("Yes\n");
  }
  return 0;
}