1 #include<cstdio>
 2 #include<cstring>
 3 #include<iostream>
 4 #include<algorithm>
 5 #define INF 1e8
 6 using namespace std;
 7
 8 int n,T,kase;
 9 int dp[205][55],t[55];
10 bool train[205][55][2];
11
12 void read(){
13     cin>>T;
14     for(int i=1;i<n;i++) cin>>t[i];
15
16     int x;cin>>x;
17     for(int i=0;i<x;i++){
18         int y;cin>>y;
19         train[y][1][0]=true;
20         int sum=0;
21         for(int j=1;j<n;j++){
22             sum=sum+t[j];
23             if(y+sum<=T) train[y+sum][j+1][0]=true;
24         }
25     }
26
27     cin>>x;
28     for(int i=0;i<x;i++){
29         int y;cin>>y;
30         train[y][n][1]=true;
31         int sum=0;
32         for(int j=n-1;j>0;j--){
33             sum=sum+t[j];
34             if(y+sum<=T) train[y+sum][j][1]=true;
35         }
36     }
37 }
38
39 void solve(){
40     for(int i=1;i<n;i++) dp[T][i]=INF;
41     dp[T][n]=0;
42     for(int i=T-1;i>=0;i--){
43         for(int j=1;j<=n;j++){
44             dp[i][j]=dp[i+1][j]+1;
45             if(j<n&&train[i][j][0]&&i+t[j]<=T) dp[i][j]=min(dp[i][j],dp[i+t[j]][j+1]);
46             if(j>1&&train[i][j][1]&&i+t[j-1]<=T) dp[i][j]=min(dp[i][j],dp[i+t[j-1]][j-1]);
47         }
48     }
49
50     cout<<"Case Number "<<++kase<<": ";
51     if(dp[0][1]>=INF) cout<<"impossible\n";
52     else cout<<dp[0][1]<<"\n";
53 }
54 int main()
55 {   kase=0;
56     while(cin>>n&&n){
57         memset(train,false,sizeof(train));
58         read();
59         solve();
60     }
61     return 0;
62 }