#include<stdio.h>
int sum(int x, int y){
  if(x%y==0){
    return x/y;
  }
  else{
    return x/y+1;
  }
}
int main(void){
  int a, b, c, d;
  scanf("%d%d%d%d",&a,&b,&c,&d);
  if(sum(c,b)<=sum(a,d)){
    printf("Yes");
  }
  else{
    printf("No");
  }
  return 0;
}