#include <stdio.h>
#include <limits.h>

#define min(x,y) (((x)<(y))?(x):(y))

int N, T, t[32], M[2], d[2][64];

/*
  On "time" and at "station",
   she'll be able to arrive at destination, with standing during "standint time"
*/
/*        time  station */
int table[ 201][     64] /* = standing time */ ;

/*
  Departure time table
*/
/*            dir  station  time */
int timetable[  2][     64][ 201] /* = arriving time */ ;

int main()
{
  int icase, i, j, k;
  int M, d;

  for (icase = 1; ; icase++) {
    scanf("%d", &N); if (N == 0) { break; }
    scanf("%d", &T);
    for (i = 0; i < N-1; i++) { scanf("%d", &t[i]); }

    for (i = 0; i < 2; i++) {
      scanf("%d", &M);
      for (j = 0; j < N; j++) {
	for (k = 0; k < T; k++) {
	  timetable[i][j][k] = -1;
	}
      }
      for (j = 0; j < M; j++) {
	scanf("%d", &d);
	if (i == 0) {
	  for (k = 0; k < N-1; k++) {
	    timetable[i][k][d] = d + t[k];
	    d += t[k];
	  }
	}
	else {
	  for (k = N-1; k > 0; k--) {
	    timetable[i][k][d] = d + t[k-1];
	    d += t[k-1];
	  }
	}
      }
    }

    for (i = 0; i < N; i++) { table[T][i] = INT_MAX; }
    table[T][N-1] = 0;
    for (i = T-1; i >= 0; i--) {
      for (j = 0; j < N; j++) {
	int candidates[3] = {INT_MAX, INT_MAX, INT_MAX};

        if (table[i+1][j] != INT_MAX) {
          candidates[0] = table[i+1][j] + 1;
        }

	if (0 <= timetable[0][j][i] && timetable[0][j][i] <= T) {
	  candidates[1] = table[timetable[0][j][i]][j+1];
	}

	if (0 <= timetable[1][j][i] && timetable[1][j][i] <= T) {
	  candidates[2] = table[timetable[1][j][i]][j-1];
	}

	table[i][j] = min(candidates[0], min(candidates[1], candidates[2]));
      }
    }
    
    printf("Case Number %d: ", icase);
    if (table[0][0] == INT_MAX) { printf("impossible\n"); }
    else { printf("%d\n", table[0][0]); }
  }
  return 0;
}