public static void main(String[] args) throws IOException {
while ((n = readInt()) != 0) {
boolean possible = false;
v = new HashSet<Integer>();
State start = new State();
for (int x = 0; x < n; x++) start.s[x].push(readInt());
int end = 0;
for (int x = 1; x <= n; x++) end += (x) * Math.pow(RADIX, x);
Queue<Pos> q = new LinkedList<Pos>();
q.offer(new Pos(toIndex(start), 0));
while (!q.isEmpty()) {
Pos curr = q.poll();
State c = toState(curr.curr);
if (curr.curr == end) {
System.out.println(curr.moves);
possible = true;
break;
}
for (int x = 0; x < n - 1; x++) {
if (c.s[x].size() == 0 && c.s[x + 1].size() == 0) continue;
if (c.s[x + 1].size() == 0) {
c.move(x, x + 1);
int ni = toIndex(c);
if (!v.contains(ni)) {
v.add(ni);
q.offer(new Pos(ni, curr.moves + 1));
}
c.move(x + 1, x);
} else if (c.s[x].size() == 0) {
c.move(x + 1, x);
int ni = toIndex(c);
if (!v.contains(ni)) {
v.add(ni);
q.offer(new Pos(ni, curr.moves + 1));
}
c.move(x, x + 1);
} else if (c.s[x].peek() < c.s[x + 1].peek()) {
c.move(x, x + 1);
int ni = toIndex(c);
if (!v.contains(ni)) {
v.add(ni);
q.offer(new Pos(ni, curr.moves + 1));
}
c.move(x + 1, x);
} else if (c.s[x].peek() > c.s[x + 1].peek()) {
c.move(x + 1, x);
int ni = toIndex(c);
if (!v.contains(ni)) {
v.add(ni);
q.offer(new Pos(ni, curr.moves + 1));
}
c.move(x, x + 1);
}
}
}
if (!possible) System.out.println("IMPOSSIBLE");
}
}
public Action absearch(State state, int d) {
int score;
int mi = 0;
int mj = 0;
alpha = Integer.MIN_VALUE;
beta = Integer.MAX_VALUE;
int best = alpha;
startTime = System.currentTimeMillis();
for (int i = 0; i < state.board.length; i++) {
for (int j = 0; j < state.board.length; j++) {
if (state.board[i][j] == 0) {
state.move(i, j, false);
score = minValue(state, d - 1);
state.undo(i, j); // undo move
// System.out.printf("%+4d", score);
if (score > best) {
mi = i;
mj = j;
best = score;
}
} // else
// System.out.print(" [] ");
// Potential random choice area. need list and PRNG
}
System.out.println();
}
// System.out.println(best);
return new Action(mi, mj);
}
public void solve() {
State currentState;
boolean isMove = false;
while (!startState.isEqual(endState)) {
int move = this.getRandomNumber();
System.out.println(move);
isMove = startState.isMoveable(move);
if (isMove) {
startState.move(move);
startState.print();
}
}
}
private int minValue(State state, int d) {
if (state.checkWin() == 1) return Integer.MAX_VALUE / 2;
if (state.checkWin() == -1) return Integer.MIN_VALUE / 2;
if (state.spaces == 0) return 0;
if (cutoff() || d <= 0) return eval(state);
int best = beta;
for (int i = 0; i < state.board.length; i++) {
for (int j = 0; j < state.board.length; j++) {
if (state.board[i][j] == 0) {
state.move(i, j, false);
best = Integer.min(best, maxValue(state, d - 1));
state.undo(i, j);
// if (best <= alpha)
// return best;
// beta = Integer.min(beta, best);
}
}
}
return best;
}