#include<stdio.h>
int main(void){
  int a,b,c,d,kai=1;
  
  scanf("%d\n %d\n %d\n %d\n",&a,&b,&c,&d);
  while(a>0&&c>0){
    if(kai%2==0){
      a=a-d;
    }
    else
      c=c-b;
    
    kai++;
  }
  if(a<=0)
    printf("No");
  else
    printf("Yes");
  
  return 0;
}