#include <stdio.h>

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