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