#include<bits/stdc++.h>using namespace std;#define pb push_back#define mp make_pair#define se second#define fs first#define ll long long#define CLR(x) memset(x,0,sizeof x)#define MC(x,y) memcpy(x,y,sizeof(x))  #define SZ(x) ((int)(x).size())#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1 #define INF 1e9typedef pair<int,int> P;const double eps=1e-9;const int maxnnode=11000;const int maxn=100100;const int mod=20071027;int has_train[205][75][2],t[75];int dp[205][75];int n,T,m1,m2,M1,M2;int main(){    int Kase=1;    while(~scanf("%d",&n)&&n){        CLR(has_train);        CLR(dp);        scanf("%d",&T);        for(int i=1;i<=n-1;i++) scanf("%d",&t[i]);        scanf("%d",&m1);        for(int i=1;i<=m1;i++)        {            scanf("%d",&M1);            for(int j=1;j<=n-1;j++)            {                if(M1<=T) has_train[M1][j][0]=1;                M1+=t[j];            }        }        scanf("%d",&m2);        for(int i=1;i<=m2;i++)        {            scanf("%d",&M2);            for(int j=n-1;j>=1;j--)            {                if(M2<=T) has_train[M2][j+1][1]=1;                M2+=t[j];            }        }        dp[T][n]=0;        for(int i=1;i<=n-1;i++) dp[T][i]=INF;        for(int i=T-1;i>=0;i--)        for(int j=1;j<=n;j++){            dp[i][j]=dp[i+1][j]+1;            if(j<n&&has_train[i][j][0]&&i+t[j]<=T) dp[i][j]=min(dp[i][j],dp[i+t[j]][j+1]);            if(j>1&&has_train[i][j][1]&&i+t[j-1]<=T) dp[i][j]=min(dp[i][j],dp[i+t[j-1]][j-1]);        }        printf("Case Number %d: ",Kase++);        if(dp[0][1]>=INF) printf("impossible\n");        else printf("%d\n",dp[0][1]);    }    return 0;}