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

int main(void) {
  int a, b ,c, d;
  scanf("%d %d %d %d", &a, &b ,&c, &d);
  float f_t = (float) a / (float) d, f_a = (float) c / (float) b;
  int count_t, count_a;
  if (f_t == (int) f_t) count_t = f_t;
  else count_t = (int) f_t + 1;
  if (f_a == (int) f_a) count_a = f_a;
  else count_a = (int) f_a + 1;
  if (count_t < count_a) printf("No\n");
  else printf("Yes\n");

  return 0;
}
