int solve()
{
    int n, m, k;
    scanf("%d %d %d", &n, &m, &k);
    char a[n][m + 1];
    for (int i = 0; i < n; ++i)
    {
        scanf(" %s", a[i]);
    }
    vector<pii> swaps(m / 2, mk(0, 2));
    int ans = 0;
    pii solo = mk(0, 0);
    if (m & 1)
    {
        solo = mk(0, 1);
        for (int i = 0; i < n; ++i)
        {
            if (a[i][m / 2] != a[n - i - 1][m / 2])
                ++solo.X;
        }
    }
    for (int i = 0; i < n; ++i)
    {
        pii cur = mk(0, 2);
        int ri = n - i - 1;
        for (int j = 0; j < m / 2; ++j)
        {
            int rj = m - j - 1;
            if (a[i][j] != a[i][rj])
                ++ans;
            if (i < n / 2)
            {
                char c1 = a[i][j];
                char c2 = a[i][rj];
                char c3 = a[ri][j];
                char c4 = a[ri][rj];
                //c1 c2
                //c3 c4
                //c1 == c2 c3 == c4
                if (c1 == c2 && c3 == c4)
                {
                    if (c1 == c3)
                        swaps[j].X += 0;
                    else
                        swaps[j].X += 2;
                }
                if (c1 == c2 && c3 != c4)
                {
                    if (c3 != c1 && c3 != c2 && c4 != c1 && c4 != c2)
                        swaps[j].X += 1;
                }
                if (c1 != c2 && c3 == c4)
                {
                    if (c1 != c3 && c1 != c4 && c2 != c3 && c2 != c4)
                        swaps[j].X += 1;
                }
                if (c1 != c2 && c3 != c4)
                {
                    if (c1 != c3 && c1 != c4 && c2 != c3 && c2 != c4)
                        swaps[j].X += 1;
                }
            }
        }
    }
    sort(all(swaps), [&](pii x, pii y)
    {
        return x.X * y.Y < y.X * x.Y;
    });
    int cr = 0;
    for (auto x : swaps)
    {
        if (cr >= k)
            break;
        if (solo.Y)
        {
            if (solo.Y + cr >= k && cr + x.Y >= k)
            {
                ans += min(x.X, solo.X);
                break;
            }
        }
        cr += x.Y;
        ans += x.X;
    }
    printf("%d\n", ans);
    return 0;
}