# include <bits/stdc++.h>
# include <atcoder/modint>
# include <atcoder/segtree>
# include <atcoder/lazysegtree>
# include <atcoder/dsu>
//# include <regex>

using namespace std;
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<vector<int>>> vvvi;
typedef vector<long long> vl;
typedef vector<vector<long long>> vvl;
typedef vector<vector<vector<long long>>> vvvl;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vector<vector<bool>>> vvvb;
#define rep(i,n) for(int i=0;i<n;i++)
#define reps(i,m,n) for(int i=m;i<n;i++)
#define repl(i,n) for(ll i=0;i<n;i++)
#define repsl(i,m,n) for(ll i=m;i<n;i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
#define repsr(i,m,n) for(int i=n-1;i>=m;i--)
#define replr(i,n) for(ll i=n-1;i>=0;i--)
#define repslr(i,m,n) for(ll i=n-1;i>=m;i--)
#define sksort(x) sort(x.begin(), x.end())
#define sksortr(x) sort(x.rbegin(), x.rend())
#define disp(x) cout << x << endl
#define disps(x) cout << x << " "
#define dispe cout << endl
#define dispv(x) for(ll xqzj=0;xqzj<(ll)x.size();xqzj++){disps(x[xqzj]);}dispe
#define dispvv(x) for(ll xqzi=0;xqzi<(ll)x.size();xqzi++){dispv(x[xqzi]);}
#define dispy cout << "Yes" << endl
#define dispn cout << "No" << endl
#define dispyn(x) if(x)dispy;else dispn
#define dispd cout << std::setprecision(20)
#define inp(x) int x;cin>>x
#define inpl(x) ll x;cin>>x
#define inps(x) string x;cin>>x
#define allv(x)  (x).begin(),(x).end()
#define allrv(x)  (x).rbegin(),(x).rend()
#define imax(x,y) x=max(x,y)
#define imin(x,y) x=min(x,y)
using mint = atcoder::modint998244353;

int main(){
    inp(n);
    inp(m);
    inp(p);
    inpl(y);
    vector<set<int>> g(n);
    map<pair<int,int>,ll> c;
    vl h(n,1000000000000000001);
    rep(i,m){
        inp(a);
        inp(b);
        g[a-1].insert(b-1);
        g[b-1].insert(a-1);
        inpl(t);
        c[{a-1,b-1}]=t;
        c[{b-1,a-1}]=t;
    }
    rep(i,p){
        inp(d);
        inpl(e);
        h[d-1]=e;
    }
    set<pair<ll,int>> st;
    st.insert({0,0});
    vl b(n,1000000000000000001);
    b[0]=0;
    while(st.size()>0){
        pair<ll,int> q=*st.begin();
        st.erase(*st.begin());
        for(int i:g[q.second]){
            ll x=q.first+c[{q.second,i}];
            if(b[i]==1000000000000000001){
                b[i]=x;
                st.insert({b[i],i});
            }else if(b[i]>x){
                st.erase({b[i],i});
                b[i]=x;
                st.insert({b[i],i});
            }
        }
    }
    ll ans=0;
    rep(i,n)imax(ans,(y-b[i])/h[i]);
    disp(ans);
}