#include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
#include <sstream>
#include <set>
#include <algorithm>
#define MAXN 8
#define reset_game(G,M) FOR(INT i = 0; i < N;i++)G[i].clear();
#define to_s(N) static_cast<ostringstream*>( &(ostringstream() << N) )->str()
USING namespace std;

struct state{
vector<int>g[MAXN];
INT d;
string id;
};

INT N,ai;
vector<int>game[MAXN];
set< string >past_game;

string to_id(vector<int>g[MAXN]){
string id;
FOR(INT i = 0; i < MAXN;i++){
string t;
FOR(INT j = 0; j < g[i].SIZE();j++){
t+= to_s(g[i][j]);
}
t+="-";
id+=t;
}
RETURN id;
}
bool game_done(vector<int>g[MAXN]){
FOR(INT i = 0; i < N;i++)
IF(g[i].empty())RETURN FALSE;
FOR(INT i = 0; i < N;i++)
IF(g[i].SIZE()!= 1 || g[i][0] != i+1)RETURN FALSE;
RETURN TRUE;
}
void print_game(vector<int>g[MAXN],INT d,string id){
printf("D:%d ;",d);cout << id << endl;
FOR(INT i = 0; i < MAXN;i++){
printf("%d:",i+1);
FOR(INT j = 0; j < g[i].SIZE();j++)printf("%d",g[i][j]);
printf("\n");
}
printf("\n");
}
INT bfs(){
queue<state> q;
q.push( (state){game[0],game[1],game[2],game[3],game[4],game[5],game[6],game[7],0,to_id(game)});
while(!q.empty()){
vector<int>g[MAXN] = q.front().g;
INT d = q.front().d;
string id = q.front().id;
q.pop();
IF(past_game.find(id) != past_game.END())
continue;
ELSE
past_game.INSERT(id);
//print_game(g,d,id);
IF(game_done(g)){
RETURN d;
}
FOR(INT i = 0; i < N;i++){
IF(g[i].empty())continue;
IF(i-1>=0){
INT left_end = g[i-1].SIZE()-1;
INT curr_end = g[i].SIZE()-1;
IF(g[i-1].empty()){
g[i-1].push_back(g[i][curr_end]);
g[i].erase(g[i].BEGIN() + curr_end);
q.push( (state){g[0],g[1],g[2],g[3],g[4],g[5],g[6],g[7],d+1,to_id(g)});
left_end++;curr_end--;
g[i].push_back(g[i-1][left_end]);
g[i-1].erase(g[i-1].BEGIN()+left_end);
}
ELSE IF(g[i-1][left_end] > g[i][curr_end]){
g[i-1].push_back(g[i][curr_end]);
g[i].erase(g[i].BEGIN() + curr_end);
q.push( (state){g[0],g[1],g[2],g[3],g[4],g[5],g[6],g[7],d+1,to_id(g)});
left_end++;curr_end--;
g[i].push_back(g[i-1][left_end]);
g[i-1].erase(g[i-1].BEGIN()+left_end);
}
}
IF(i+1<N){
INT rght_end = g[i+1].SIZE()-1;
INT curr_end = g[i].SIZE()-1;
IF(g[i+1].empty()){
g[i+1].push_back(g[i][curr_end]);
g[i].erase(g[i].BEGIN() + curr_end);
q.push( (state){g[0],g[1],g[2],g[3],g[4],g[5],g[6],g[7],d+1,to_id(g)});
rght_end++;curr_end--;
g[i].push_back(g[i+1][rght_end]);
g[i+1].erase(g[i+1].BEGIN()+rght_end);
}
ELSE IF(g[i+1][rght_end] > g[i][curr_end]){
g[i+1].push_back(g[i][curr_end]);
g[i].erase(g[i].BEGIN() + curr_end);
q.push( (state){g[0],g[1],g[2],g[3],g[4],g[5],g[6],g[7],d+1,to_id(g)});
rght_end++;curr_end--;
g[i].push_back(g[i+1][rght_end]);
g[i+1].erase(g[i+1].BEGIN()+rght_end);
}
}
}
}
RETURN -1;
}
INT main(){
//freopen("input.txt","r",stdin);
while(scanf("%d",&N)&& N!= 0){
FOR(INT i = 0; i < N;i++){
scanf("%d",&ai);
game[i].push_back(ai);
}
//print_game(game,0,to_id(game));
INT ans = bfs();
IF(ans == -1)printf("IMPOSSIBLE\n");
ELSE         printf("%d\n",ans);
past_game.clear();
reset_game(game,MAXN);
}
RETURN 0;
}