#include <stdio.h>
 
int main(void){
  int a,b,c,d,i;
  int count1=0;
  int count2=0;
  scanf("%d %d %d %d", &a, &b, &c, &d);

  for(i=0; c>0; i++){
    c -= b;
    count1++;
  }
  for(i=0; a>0; i++){
    a -= d;
    count2 ++;
  }

  if(count2<=count1)
  printf("Yes");
  else
  printf("No");
  
  
  return 0;
}