#nullable enable

using System.Numerics;

object? Solve()
{
    var n = Int();
    var m = Int();
    var p = Int();
    var y = long.Parse(String());
    var adjl = new Memory<(int, long)>[n].AsSpan();
    {
        var adjlo = n.Repeat(() => new List<(int, long)>());
        for (var i = 0; i < m; i++)
        {
            var u = Int() - 1;
            var v = Int() - 1;
            var c = Int();
            adjlo[u].Add((v, c));
            adjlo[v].Add((u, c));
        }
        for (var i = 0; i < n; i++) adjl[i] = adjlo[i].ToArray();
    }
    var shops = new int[n].AsSpan();
    shops.Fill(int.MaxValue);
    for (var i = 0; i < p; i++) shops[Int() - 1] = Int();

    bool F(long x, Span<int> shops, Span<Memory<(int, long)>> adjl)
    {
        var q = new PriorityQueue<(int v, long yl), long>();
        var byz = new long[n].AsSpan();
        q.Enqueue((0, y), -y);
        byz[0] = y;
        while (q.Count > 0)
        {
            var (v, yl) = q.Dequeue();
            if (yl < byz[v]) continue;
            if (yl / x >= shops[v]) return true;
            var adjz = adjl[v].Span;
            foreach (var (next, c) in adjz)
            {
                var ny = Math.Max(yl - c, 0);
                if (byz[next] < ny)
                {
                    byz[next] = ny;
                    q.Enqueue((next, ny), -ny);
                }
            }
        }
        return false;
    }
    var pass = 0L;
    var fail = y + 1;
    while (Math.Abs(pass - fail) > 1)
    {
        var middle = (pass + fail) >> 1;
        if (F(middle, shops, adjl)) pass = middle; else fail = middle;
    }
    return pass;
}

#region
AtCoderIO _io_;
var _backend_ = new StandardIOBackend();
_io_ = new(){ Backend = _backend_ };
Out(Solve());
_backend_.Flush();

string String() => _io_.Next();
int Int() => int.Parse(String());
void Out(object? x, string? sep = null) => _io_.Out(x, sep ?? Environment.NewLine);

class AtCoderIO
{
    public required StandardIOBackend Backend { get; init; }

    Memory<string> _input = Array.Empty<string>();
    int _iter = 0;
    public string Next()
    {
        while (_iter >= _input.Length) (_input, _iter) = (Backend.ReadLine().Trim().Split(' '), 0);
        return _input.Span[_iter++];
    }

    public void Out(object? x, string separator)
    {
        if (x == null) return;
        if (x is System.Collections.IEnumerable a and not string)
        {
            var objects = a.Cast<object>();
            if (!objects.Any()) return;
            x = string.Join(separator, objects);
        }
        Backend.WriteLine(x);
    }
}

class StandardIOBackend
{
    readonly StreamReader _sr = new(Console.OpenStandardInput());
    readonly StreamWriter _sw = new(Console.OpenStandardOutput()) { AutoFlush = false };
    public string ReadLine() => _sr.ReadLine()!;
    public void WriteLine(object? value) => _sw.WriteLine(value);
    public void Flush() => _sw.Flush();
}
#endregion

static class Extensions
{
    public static T[] Repeat<T>(this int time, Func<T> F) => Enumerable.Range(0, time).Select(_ => F()).ToArray();
}