#include <bits/stdc++.h>

using namespace std; const int maxn = 2e3 + 5;

int n;

char A[maxn][maxn];

int a[maxn][maxn], b[maxn][maxn];

int ans;

int c[maxn];

void work()
{
    for (int i = 1; i <= n << 1; i++)
    {
        int s = 0;
        for (int j = 1; j <= n << 1; j++) s += a[i][j];
        // cerr << s << endl;
        if (s != n)
        {
            ans += maxn << 1;
            return;
        }
    }
    for (int i = 1; i <= n << 1; i++)
    {
        bool A = 1, B = 1;
        for (int j = 1; j <= n << 1; j++) A &= (a[1][j] == a[i][j]);
        for (int j = 1; j <= n << 1; j++) B &= (a[1][j] != a[i][j]);
        if (!(A ^ B))
        {
            ans += maxn << 1;
            return;
        }
        c[i] = A;
    }
    int P = 0, Q = 0;
    for (int i = 1; i <= n << 1; i++) P += (c[i] == (i & 1));
    for (int i = 1; i <= n << 1; i++) Q += (c[i] != (i & 1));
    ans += (min(P, Q) >> 1);
}

inline void solve()
{
    scanf("%d", &n);
    for (int i = 1; i <= n << 1; i++)
    {
        scanf("%s", A[i] + 1);
        for (int j = 1; j <= n << 1; j++) a[i][j] = A[i][j] - '0';
    }
    ans = 0;
    work();
    for (int i = 1; i <= n << 1; i++) for (int j = 1; j <= n << 1; j++) b[i][j] = a[i][j];
    for (int i = 1; i <= n << 1; i++) for (int j = 1; j <= n << 1; j++) a[i][j] = b[j][i];
    work();
    if (ans >= maxn << 1) puts("IMPOSSIBLE");
    else printf("%d\n", ans);
}

int main()
{
    int Tt; scanf("%d", &Tt); for (int i = 1; i <= Tt; i++) printf("Case #%d: ", i), solve();
    return 0;
}