#include<stdio.h>

void main(){
  int a, b, c, d;
  scanf("%d %d %d %d",&a ,&b, &c, &d);
  
  while(1){
    c -= b;
    if(c<=0)
      break;
    a -= d;
    if(a<=0)
      break;    
  }
  if(a>0)
    printf("Yes");
  else
    printf("No");
}