#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()!.Split(' '), 0);
    return T.Parse(_input[_iter++], null);
}
#endregion

var n = I<int>();
if (n < 3)
{
    Console.WriteLine(-1);
    return;
}
var sns = new HashSet<(int, int)>();
var m = n * n;
for (var i = 0; i < m; i++)
{
    for (var j = -2; j <= 2; j++)
    {
        if (j == 0) continue;
        var t = (i + j + m) % m;
        var min = Math.Min(i, t);
        var max = Math.Max(i, t);
        sns.Add((min, max));
    }
}
var ans = new List<string>();
foreach (var (u, v) in sns) ans.Add((u + 1) + " " + (v + 1));
Console.WriteLine(ans.Count);
Console.WriteLine(string.Join(Environment.NewLine, ans));