#include<stdio.h>
int main()
{
  int a,b,c,d;
  int n1=1;
  int n2=1;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  while(a-d*n1>0) {
    n1++;
  }
  while(c-b*n2>0) {
    n2++;
  }
  if (n1<=n2) printf("Yes");
  else printf("No");
  return 0;
}