use std::cmp::Reverse;

use proconio::input;

fn main() {
    input! {
        n: usize,
        m: usize,
        p: usize,
        y: u64,
        abc: [(usize, usize, u64); m],
        de: [(usize, u64); p],
    }

    let mut adj_list = vec![vec![]; n];

    for &(ai, bi, ci) in &abc {
        adj_list[ai - 1].push((bi - 1, ci));
        adj_list[bi - 1].push((ai - 1, ci));
    }

    let mut queue = std::collections::BinaryHeap::new();
    let mut dist = vec![u64::MAX; n];
    queue.push((Reverse(0), 0));

    while let Some((Reverse(d), u)) = queue.pop() {
        if dist[u] != u64::MAX {
            continue;
        }
        dist[u] = d;
        for &(v, cv) in &adj_list[u] {
            if dist[v] == u64::MAX {
                queue.push((Reverse(d + cv), v));
            }
        }
    }
    let mut ans = 0;
    for &(di, ei) in &de {
        ans = ans.max(y.saturating_sub(dist[di - 1]) / ei);
    }

    println!("{ans}");
}