#include<stdio.h>
int main(void)
{
  int a,b,c,d;
  scanf("%d%d%d%d", &a, &b, &c, &d);
  while (1)
  {
    c = c - b;
    if (c <= 0){
      printf("Yes");
      return 0;}
    a = a - d;
    if (a <= 0){
      printf("No");
      return 0;}
  }
  return 0;
}