#include <stdio.h>

int main()
{
  int aa, bb, cc, dd, ii = 0;
  scanf("%d %d %d %d", &aa, &bb, &cc, &dd);
  while(1)
  {
    ii++;
    if(cc <= ii * bb)
    {
      puts("Yes");
      return 0;
    }
    else if(aa <= ii * dd)
    {
      puts("No");
      return 0;
    }
  }
  return 0;
}