#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using mint = atcoder::modint998244353;
using maxt = atcoder::modint1000000007;
//ここからグラフ探索系
using Graph = vector<vector<int>>;
struct edge {
  int to;
  ll cost;
};
using Cost_Graph = vector<vector<edge>>;
using D_heap = priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>>;
//グラフ探索系終わり
vector<ll> Era(int N) {
  vector<ll> ans(0, 0);
  vector<bool> isprime(N + 1, true);
  isprime.at(1) = false;
  for(int i = 1; i <= N; i++) {
    if(isprime.at(i)) {
      ans.push_back(i);
      for(int j = 2 * i; j <= N; j += i) {
        isprime.at(j) = false;
      }
    }
  }
  return ans;
}
ll POW(ll a, int N) {
  if(N == 0) {
    return 1;
  }
  if(N == 1) {
    return a;
  }
  ll ans = POW(a, N / 2) * POW(a, N / 2);
  if(N % 2 == 1) {
    ans *= a;
  }
  return ans;
}
ll GCD(ll a, ll b) {
  if(b == 0) {
    return a;
  }
  int r = a % b;
  return GCD(b, r);
}
ll LCM(ll a, ll b) {
  return (a * b) / GCD(a, b);
}
vector<ll> zaatu(vector<ll> a) {
  vector<ll> b(0, 0);
  b = a;
  sort(b.begin(), b.end());
  b.erase(unique(b.begin(), b.end()), b.end());
  int s = b.size();
  for(ll &o : a) {
    int l = 0, r = s, c = 0;
    while(r - l > 1) {
      c = (l + r) / 2;
      if(b.at(c) <= o) {
        l = c;
      }
      else {
        r = c;
      }
    }
    o = r;
  }
  return a;
}
struct FenwickTree {
  int N;
  vector<ll> a;
  
  FenwickTree(int n) {
    N = n;
    a.assign(N + 1, 0);
  }
  
  void add(int i, ll x) {
    for(int j = i; j <= N; j += (j & -j)) {
      a.at(j) += x;
    }
  }
  
  ll sum(int i, int j) {
    return sum_sub(j) - sum_sub(i - 1);
  }
  
  ll sum_sub(int i) {
    if(i == 0) {
      return 0;
    }
    ll s = 0;
    for(int j = i; j > 0; j -= (j & -j)) {
      s += a.at(j);
    }
    return s;
  }
};
ll tento(vector<ll> a) {
  int s = a.size();
  FenwickTree tmp(s);
  ll ans = 0;
  for(int i = 0; i < s; i++) {
    ans += i - tmp.sum_sub(a.at(i));
    tmp.add(a.at(i), 1);
  }
  return ans;
}
//__builtin_popcount
//next_permutation
//srand((unsigned)time(NULL))
//cout << fixed << setprecision(Digit);
//library end

vector<ll> dist(200010, -1LL);
int main() {
  int N, M, P;
  ll Y;
  cin >> N >> M >> P >> Y;
  Cost_Graph G(N + 1, vector<edge>(0));
  for(int i = 0; i < M; i++) {
    int now;
    edge e;
    cin >> now >> e.to >> e.cost;
    G.at(now).push_back(e);
  }
  D_heap que;
  que.push(make_pair(0LL, 1));
  while(!que.empty()) {
    pair<ll, int> v = que.top();
    que.pop();
    if(dist.at(v.second) != -1LL) {
      continue;
    }
    dist.at(v.second) = v.first;
    for(edge next_v : G.at(v.second)) {
      if(dist.at(next_v.to) == -1LL) {
        que.push(make_pair(v.first + next_v.cost, next_v.to));
      }
    }
  }
  ll ans = 0;
  for(int i = 0; i < P; i++) {
    int D;
    ll E;
    cin >> D >> E;
    if(dist.at(D) != -1LL && dist.at(D) <= Y) {
      ans = max(ans, (Y - dist.at(D)) / E);
    }
  }
  cout << ans << endl;
}