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