#nullable enable

#region
var (_input, _iter) = (Array.Empty<string>(), 0);
T I<T>() where T : IParsable<T>
{
    while (_iter >= _input.Length) (_input, _iter) = (Console.ReadLine()!.Trim().Split(' '), 0);
    return T.Parse(_input[_iter++], null);
}
#endregion

var n = I<int>();
var m = I<int>();
var gz = new bool[n][,];
for (var i = 0; i < n; i++)
{
    var g = new bool[m, m];
    for (var j = 0; j < m; j++)
    {
        var str = I<string>();
        for (var k = 0; k < m; k++) g[j, k] = str[k] == '#';
    }
    gz[i] = g;
}
var b = 1 << (n * 2);
var ans = m * m;
for (var s = 0; s < b; s++)
{
    var sg = new bool[m, m];
    var cs = s;
    for (var i = 0; i < n; i++)
    {
        var r = cs & 3;
        cs >>= 2;
        var g = gz[i];
        while (r-- > 0) g = g.Rotated();
        for (var j = 0; j < m; j++) for (var k = 0; k < m; k++) sg[j, k] |= g[j, k];
    }
    var sns = 0;
    for (var j = 0; j < m; j++) for (var k = 0; k < m; k++) if (sg[j, k]) sns++;
    ans = Math.Min(ans, sns);
}
Console.WriteLine(ans);

static class Extensions
{
    public static T[,] Rotated<T>(this T[,] g)
    {
        var (h, w) = (g.GetLength(0), g.GetLength(1));
        var res = new T[w, h];
        for (var i = 0; i < h; i++) for (var j = 0; j < w; j++) res[w - 1 - j, i] = g[i, j];
        return res;
    }
}