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

int main() {
  int a, b, c, d;
  scanf("%d %d %d %d", &a, &b, &c, &d);
  int n1= c/b + 1;
  if(c%b==0) n1--;
  int n2= a/d + 1;
  if(a%d==0) n2--;
  
  if(n2>=n1) printf("Yes");
  else printf("No");
  return 0;

}
