#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

static T[] Range<T>(int n, Func<T> F) => Enumerable.Range(0, n).Select(_ => F()).ToArray();

var n = I<int>();
var k = I<int>();
var pz = Range(n, I<int>);

var ans = new List<string>();
for (var s = 0; s < k; s++)
{
    var f = true;
    while (f)
    {
        f = false;
        for (var i = s; i + k < n; i += k)
        {
            var j = i + k;
            if (pz[i] > pz[j])
            {
                (pz[i], pz[j]) = (pz[j], pz[i]);
                ans.Add((i + 1) + " " + (j + 1));
                f = true;
            }
        }
    }
}
for (var i = 0; i < n; i++) if (pz[i] != i + 1)
{
    Console.WriteLine(-1);
    return;
}
Console.WriteLine(ans.Count);
Console.WriteLine(string.Join(Environment.NewLine, ans));