 
#include <stdio.h>
int main(void)
{
  int A,B,C,D;
 
  scanf("%d",&A);
  scanf("%d",&B);
  scanf("%d",&C);
  scanf("%d",&D);
  
  do{
    C=C-B;
    if(C<=0)
      break;
    else
      B=B-D;
  }while(B>0);
  
  if(C<=0)
    printf("Yes");
  else
    printf("No");
  
  return 0;
}