#include <cassert>// c
#include <iostream>// io
#include <iomanip>
#include <fstream>
#include <sstream>
#include <vector>// container
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <algorithm>// other
#include <complex>
#include <numeric>
#include <functional>
#include <random>
#include <regex>
using namespace std;

typedef long long ll;

#define ALL(c) (begin(c)),(end(c))
#define REP(i,n) FOR(i,0,n)
#define REPr(i,n) FORr(i,0,n)
#define FOR(i,l,r) for(int i=(int)(l);i<(int)(r);++i)
#define FORr(i,l,r) for(int i=(int)(r)-1;i>=(int)(l);--i)
#define EACH(it,o) for(auto it = (o).begin(); it != (o).end(); ++it)
#define IN(l,v,r) ((l)<=(v) && (v)<(r))
#define UNIQUE(v) v.erase(unique(ALL(v)),v.end())
//debug
#define DUMP(x)  cerr << #x << " = " << (x)
#define LINE()    cerr<< " (L" << __LINE__ << ")"

class range {
private:
	struct Iter{
		int v;
		int operator*(){return v;}
		bool operator!=(Iter& itr) {return v < itr.v;}
		void operator++() {++v;}
	};
	Iter i, n;
public:
	range(int n) : i({0}), n({n}) {}
	range(int i, int n) : i({i}), n({n}) {}
	Iter& begin() {return i;}
	Iter& end() {return n;}
};

//output
template<typename T> ostream& operator << (ostream& os, const vector<T>& as){REP(i,as.size()){if(i!=0)os<<" "; os<<as[i];}return os;}
template<typename T> ostream& operator << (ostream& os, const vector<vector<T>>& as){REP(i,as.size()){if(i!=0)os<<endl; os<<as[i];}return os;}
template<typename T> ostream& operator << (ostream& os, const set<T>& ss){for(auto a:ss){if(a!=ss.begin())os<<" "; os<<a;}return os;}
template<typename T1,typename T2> ostream& operator << (ostream& os, const pair<T1,T2>& p){os<<p.first<<" "<<p.second;return os;}
template<typename K,typename V> ostream& operator << (ostream& os, const map<K,V>& m){bool isF=true;for(auto& p:m){if(!isF)os<<endl;os<<p;isF=false;}return os;}
template<typename T1> ostream& operator << (ostream& os, const tuple<T1>& t){os << get<0>(t);return os;}
template<typename T1,typename T2> ostream& operator << (ostream& os, const tuple<T1,T2>& t){os << get<0>(t)<<" "<<get<1>(t);return os;}
template<typename T1,typename T2,typename T3> ostream& operator << (ostream& os, const tuple<T1,T2,T3>& t){os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t);return os;}
template<typename T1,typename T2,typename T3,typename T4> ostream& operator << (ostream& os, const tuple<T1,T2,T3,T4>& t){os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t)<<" "<<get<3>(t);return os;}
template<typename T1,typename T2,typename T3,typename T4,typename T5> ostream& operator << (ostream& os, const tuple<T1,T2,T3,T4,T5>& t){os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t)<<" "<<get<3>(t)<<" "<<get<4>(t);return os;}
template<typename T1,typename T2,typename T3,typename T4,typename T5,typename T6> ostream& operator << (ostream& os, const tuple<T1,T2,T3,T4,T5,T6>& t){os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t)<<" "<<get<3>(t)<<" "<<get<4>(t)<<" "<<get<5>(t);return os;}
template<typename T1,typename T2,typename T3,typename T4,typename T5,typename T6,typename T7> ostream& operator << (ostream& os, const tuple<T1,T2,T3,T4,T5,T6,T7>& t){os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t)<<" "<<get<3>(t)<<" "<<get<4>(t)<<" "<<get<5>(t)<<" "<<get<6>(t);return os;}

//input
char tmp[1000];
#define nextInt(n) scanf("%d",&n)
#define nextLong(n) scanf("%lld",&n) //I64d
#define nextDouble(n) scanf("%lf",&n) 
#define nextChar(n) scanf("%c",&n)
#define nextString(n) scanf("%s",tmp);n=tmp

// values
template<typename T> T INF(){assert(false);};
template<> int INF<int>(){return 1<<28;};
template<> ll INF<ll>(){return 1LL<<58;};
template<> double INF<double>(){return 1e16;};

template<class T> T EPS(){assert(false);};
template<> int EPS<int>(){return 1;};
template<> ll EPS<ll>(){return 1LL;};
template<> double EPS<double>(){return 1e-8;};
template<> long double EPS<long double>(){return 1e-8;};


template<typename T,typename U> T pmod(T v,U M){return (v%M+M)%M;}


typedef int Cost; Cost CINF=1<<28;
struct Edge{
	int f,t;Cost c;
	Edge(int f,int t,Cost c) : f(f),t(t),c(c) {};
	bool operator<(Edge r) const{return c<r.c;}
	bool operator>(Edge r) const{return c>r.c;}
};
typedef vector<vector<Edge> >  Graph;

struct Task{
    int prev,pos;Cost c;
    Task(int prev,int pos,Cost c)
        :prev(prev),pos(pos),c(c){};
    bool operator>(const Task& r) const{ return c > r.c;}
};
vector<Cost> dijkstra(const Graph& g,const int s,vector<int>& prev){
    const int V=g.size();
    vector<Cost> d(V,CINF);d[s]=0;
    fill(ALL(prev), -2);
    
    priority_queue<Task,vector<Task>,greater<Task> > que;que.push(Task(-1,s,0));// [ ,e,,f, ] <=> e.cost < e.cost
    vector<bool> visited(V);
    while(!que.empty()){
        Task task=que.top();que.pop();
        if(visited[task.pos])continue;
        visited[task.pos]=true;
        prev[task.pos]=task.prev;
        EACH(e,g[task.pos])if(d[e->t]>d[e->f]+e->c){
            d[e->t]=d[e->f]+e->c;
            que.push(Task(e->f,e->t,d[e->t]));
        }   
    }
    return d;
}
vector<Cost> dijkstra(const Graph& g,const int s){
    vector<int> prev(g.size());return dijkstra(g,s,prev);
}

class Main{
	public:

	void run(){

		while(true){
			int n,m,l,s,t;cin >> n >> m >> l >> s >> t;if(n==0)break;
			s--;
			vector<vector<int>> g(n,vector<int>(n,INF<int>()));
			REP(i,n)g[i][i]=0;
			REP(i,m){
				int a,b,c;cin >> a >> b >> c;a--;b--;
				g[a][b]=g[b][a]=c;
			}
			REP(k,n)REP(i,n)REP(j,n)
				g[i][j]=min(g[i][j],g[i][k]+g[k][j]);

			js.clear();
			REP(i,l){
				int v,e;cin >> v >> e;v--;
				js[v]=e;
			}
			enc.clear();EACH(it,js)enc[it->first]=0;enc[s]=0;
			N=0;EACH(it,enc)enc[it->first]=N++;
			dec.clear();EACH(it,enc)dec[it->second]=it->first;

			ds = vector<vector<int>>(N,vector<int>(N));
			EACH(i,dec)EACH(j,dec)
				ds[i->first][j->first]=g[i->second][j->second];
				

			dp =vector<vector<int>>(N,vector<int>(1<<N,INF<int>()));
			dp[enc[s]][0]=0;
			REP(i,N)REP(bit,1<<N)rec(i,bit);

			int Mv=0;
			REP(i,N)REP(bit,1<<N)if(dp[i][bit]+ds[i][enc[s]]<=t){
				int bc=0;REP(k,N)if(bit&(1<<k))bc++;
				Mv=max(Mv,bc);
			}
			cout << Mv <<endl;
		}
	}
	
	map<int,int> js;
	map<int,int> enc;
	map<int,int> dec;
	vector<vector<int>> dp;
	vector<vector<int>> ds;
	int N;
	int rec(int i,int bit){
		if(dp[i][bit]!=INF<int>())return dp[i][bit];
		dp[i][bit]=INF<int>()-1;
		if(((bit>>i)&1) && js.count(dec[i])){
			REP(j,N)dp[i][bit]=min(dp[i][bit],rec(j,bit-(1<<i))+ds[j][i]+js[dec[i]]);
		}
		return dp[i][bit];
	}
};

int main(){
	cout <<fixed<<setprecision(20);
	cin.tie(0);
	ios::sync_with_stdio(false);
	Main().run();
	return 0;
}

Measured memory_bytes: 19384