wa

#include <bits/stdc++.h>

using namespace std;

typedef long long   LL;
#define pii         pair<int,int>
#define pll         pair<LL,LL>
#define vi      vector<int>
#define SYNC        ios_base::sync_with_stdio(0)
#define CT      cin.tie(0)
#define sf(a)       scanf("%d", &a)
#define sll(a)      scanf("%lld", &a)
#define sff(a, b)   scanf("%d %d", &a, &b)
#define sfff(a,b,c) scanf("%d %d %d", &a, &b, &c)
#define debug       printf("Here\n")
#define PI      acos(-1)
#define all(x)      x.begin(),x.end()
#define mem(x, val)     memset((x),val,sizeof((x)))
#define xx      first
#define yy      second
#define pb      push_back
#define _max(a,b,c)     max(a, max(b, c))
#define _min(a,b,c)     min(a, min(b, c))
#define INF         INT_MAX
#define MOD         1000000007
#define NN      100005

int setBit(int n, int pos) { return n = n | (1 << pos); }
int resetBit(int n, int pos) { return n = n & ~(1 << pos); }
bool checkBit(int n, int pos) { return (bool)(n & (1 << pos)); }

int s[80][80];
bool vis[80][80];
LL dp[80][80][10][5];
int n, k;
LL maxx;

bool valid(int x, int y) {
    return (x > 0 && y > 0 && x <= n && y <= n);
}

int dx[] = {1,0, 0};
int dy[] = {0,-1,1};

void dfs(int x, int y, int cnt, LL sum) {
    if(cnt > k) return;
    if(x == n && y == n) {
        maxx = max(sum, maxx);
        return;
    }
    for(int i = 0; i < 3; i++) {
        int xx = x + dx[i], yy = y + dy[i];
        if(valid(xx, yy) && !vis[xx][yy]) {
            vis[xx][yy] = true;
            if(s[xx][yy] < 0 && dp[xx][yy][cnt + 1][i] < sum + s[xx][yy]) {
                dp[xx][yy][cnt + 1][i] = sum + s[xx][yy];
                dfs(xx, yy, cnt + 1, sum + s[xx][yy]);
            } else if(s[xx][yy] >= 0 && dp[xx][yy][cnt][i] < sum + s[xx][yy]) {
                dp[xx][yy][cnt][i] = sum + s[xx][yy];
                dfs(xx, yy, cnt, sum + s[xx][yy]);
            }
            vis[xx][yy] = false;
        }
    }
}

int main() {
    int cs = 1;
    while(sff(n, k) == 2 && n)) {
        for(int i = 1; i <= n; i++) {
            for(int j = 1; j <= n; j++) {
                sf(s[i][j]);
            }
        }
        maxx = -INF;
        mem(vis, false);
        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++)
                for(int k = 0; k < 6; k++)
                    for(int d = 0; d < 3; d++)
                        dp[i][j][k][d] = -INF;
        vis[1][1] = true;
        dfs(1, 1, s[1][1] < 0, s[1][1]);
        printf("Case %d: ", cs++);
        maxx == -INF? puts("impossible") : printf("%lld\n", maxx);

    }
    return 0;
}