uva 1025

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <cstdlib>
#include <stack>
#include <cctype>
#include <string>
#include <queue>
#include <map>
#include <set>

using namespace std;

const int INF = 0xffffff;
const double ESP = 10e-8;
const double Pi = 4 * atan(1.0);
const int MAXN =  200 + 10;
const long long mod =  1000000007;
const int dr[] = {1,0,-1,0,-1,1,-1,1};
const int dc[] = {0,1,0,-1,1,-1,-1,1};
typedef long long LL;

LL gac(LL a,LL b){
    return b?gac(b,a%b):a;
}

int dp[210][MAXN];
int n,T;
int t[MAXN];
int M1,M2;
int d[MAXN];
int e[MAXN];
bool has_train[210][MAXN][2];

int main(){
#ifndef ONLINE_JUDGE
    freopen("input.in","r",stdin);
   // freopen("output.txt","w",stdout);
#endif
    int cas = 1;
    while(~scanf("%d",&n) && n){
    scanf("%d",&T);
    for(int i = 2;i <= n;i++){
        scanf("%d",&t[i]);
    }
    t[1] = 0;
    t[n+1] = 0;
    memset(has_train,0,sizeof(has_train));
    scanf("%d",&M1);
    for(int i = 1;i <= M1;i++){
        scanf("%d",&d[i]);
        int sum = d[i];
        for(int j = 1;j <= n;j++){
            sum += t[j];
            has_train[sum][j][0] = 1;
        }
    }
    scanf("%d",&M2);
    for(int i = 1;i <= M2;i++){
        scanf("%d",&e[i]);
        int sum = e[i];
        for(int j = n;j > 0;j--){
            sum += t[j+1];
            has_train[sum][j][1] = 1;
        }
    }
    for(int i = 1;i < n;i++){
        dp[T][i] = INF;
    }
    dp[T][n] = 0;
    for(int i = T-1;i > -1;i--){
        for(int j = 1;j <= n;j++){
            dp[i][j] = dp[i+1][j] + 1;//等待下一个单位
            if(j < n && has_train[i][j][0] && i + t[j+1] <= T){ // 从左到右有可以搭乘的车
                dp[i][j] = min(dp[i][j],dp[i+ t[j+1]][j+1]);
            }
            if(j > 1 && has_train[i][j][1] && i + t[j] <= T){//从右到左有可以搭乘的车
                dp[i][j] = min(dp[i][j],dp[i+t[j] ][j-1]);
            }
        }
    }
    printf("Case Number %d: ",cas++);
    if(dp[0][1] >= INF){
        printf("impossible\n");
    }
    else{
        printf("%d\n",dp[0][1]);
    }
    }
    return 0;
}