use std::{cmp::Reverse, collections::BinaryHeap};

#[allow(non_snake_case)]

use proconio::input;
use proconio::marker::Usize1;

const INF: i64 = 1_000_000_000_000_000_000;

fn main() {
    input! {
        N: usize, M: usize, P: usize, Y: i64,
        roads: [(Usize1, Usize1, i64); M],
        shops: [(Usize1, i64); P],
    }

    let mut graph = vec![vec![]; N];
    for &(u, v, w) in &roads {
        graph[u].push((v, w));
        graph[v].push((u, w));
    }

    let mut dist = vec![INF; N];
    dist[0] = 0;

    let mut pq = BinaryHeap::<(Reverse<i64>, usize)>::new();
    pq.push((Reverse(0), 0));

    while let Some((Reverse(d), u)) = pq.pop() {
        if dist[u] < d {
            continue;
        }
        for &(v, w) in &graph[u] {
            if dist[v] > d + w {
                dist[v] = d + w;
                pq.push((Reverse(d + w), v));
            }
        }
    }

    let mut ans = 0;
    for &(d, e) in &shops {
        let money = 0.max(Y - dist[d]);
        ans = ans.max(money / e);
    }

    println!("{ans}");
}