/**
 * 數三退一
 * @author Lei
 * @version 建立時間：2009-8-17 上午11:13:18
 */
public class Count3Quit {
 public static void main(String[] args) {
  KidCircle kc = new KidCircle(500);
  int kidNumber = 0;
  Kid kid = kc.first;
  while(kc.count > 1) {
   kidNumber ++;
   if(kidNumber ==3) {
    kidNumber = 0;
    kc.delKid(kid);
   }
   kid = kid.rightKid;
  }
  System.out.println(kc.first.id);
  
 }
}

class Kid {
 int id;
 Kid leftKid;//左邊的人
 Kid rightKid;//右邊的人
}

class KidCircle {
 int count = 0;
 Kid first, last;//第一個人和最後一個人
 public KidCircle(int kidNumber) {
  for(int i = 0; i< kidNumber; i ++) {
   addKid();
  }
 }
 
 public void addKid() {
  Kid kid = new Kid();
  kid.id = count;
  if(count <= 0) {
   first = kid;
   last = kid;
   kid.leftKid = kid;
   kid.rightKid = kid;
  } else {
   last.rightKid = kid;
   kid.leftKid = last;
   kid.rightKid = first;
   first.leftKid = kid;
   last = kid;
  }
  count ++;
 }
 
 public void delKid(Kid kid) {
  if(count <= 0) {
   return;
  }else if(1 == count) {
   first = last = null;
  } else {
   kid.rightKid.leftKid = kid.leftKid;
   kid.leftKid.rightKid = kid.rightKid;
   if(first == kid) {
    first = kid.rightKid;
   } else if(last == kid) {
    last = kid.leftKid;
   }
  }
  count --;
 }
}