#nullable enable

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

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

var n = I<int>();
var x = I<int>();
var g = Range(n, () => new List<int>());
for (var i = 1; i < n; i++)
{
    var p = I<int>() - 1;
    g[p].Add(i);
}
var cz = new int[n];
var sz = new int[n];
for (var i = 1; i < n; i++)
{
    cz[i] = I<int>();
    sz[i] = I<int>();
}

Dictionary<int, long> S(int v)
{
    var s = sz[v];
    var c = cz[v];
    var d = new Dictionary<int, long>(){ [s] = c };
    foreach (var u in g[v])
    {
        var next = S(u);
        var nd = new Dictionary<int, long>();
        foreach (var (ik, iv) in d) foreach (var (jk, jv) in next)
        {
            var nc = iv + jv;
            var k = Math.Min(ik + jk, x);
            if (nd.TryGetValue(k, out var cv) && cv <= nc) continue;
            nd[k] = nc;
        }
        d = nd;
    }
    d[0] = 0;
    return d;
}
var ans = S(0);
Console.WriteLine(ans[x]);