#include <stdio.h>
int main(void){
  int a,b,c,d,t,k;
  scanf("%d", &a);
  scanf("%d", &b);
  scanf("%d", &c);
  scanf("%d", &d);
  t=c/b;
  k=a/d;
  if(t>k)
    printf("Yes\n");
  else if(t<=k)
    printf("No\n");
  return 0;
}