int main(void) {
  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)
    printf("No\n");
  else
    printf("Yes\n");
  return 0;
}