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