#include <iostream>
#include <cstdio>
#include <iomanip>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <utility>
#include <numeric>
#include <algorithm>
#include <functional>
#include <cctype>
#include <complex>
#include <string>
#include <sstream>
#include <fstream>
#include <cassert>
using namespace std;

//common
typedef long long i64,ll;

#define BR "\n"
#define ALL(c) (c).begin(),(c).end()
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define FOR(i,l,r) for(int i=(l);i<(int)(r);++i)
#define EACH(it,o) for(auto it = (o).begin(); it != (o).end(); ++it)
#define IN(l,v,r) ((l)<=(v) && (v)<(r))

//debug
#ifdef NDEBUG
#define DUMP(x)
#define DUMPLN(x)
#define DEBUG(x)
#define DEBUGLN(x)
#define LINE()
#define LINELN()
#define CHECK(exp,act)
#define STOP(e)
#else
#define DUMP(x)  cerr << #x << " = " << (x)
#define DUMPLN(x)  DUMP(x) <<endl
#define DEBUG(x) DUMP(x) << LINE() << " " << __FILE__
#define DEBUGLN(x) DEBUG(x)<<endl
#define LINE()    cerr<< " (L" << __LINE__ << ")"
#define LINELN()    LINE()<<endl
#define CHECK(exp,act)  if(exp!=act){DUMPLN(exp);DEBUGLN(act);}
#define STOP(e)  CHECK(e,true);if(!(e)) exit(1);
#endif

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

template<typename T,typename V> inline T pmod(T v,V MOD){
	return (v%MOD+MOD)%MOD;
}

template<class T> inline string toString(const vector<T>& x) {
	stringstream ss;
	REP(i,x.size()){
		if(i!=0)ss<<" ";
		ss<< x[i];
	}
	return ss.str();
}
template<class T> inline string toString(const vector<vector<T> >& map) {
	stringstream ss;
	REP(i,map.size()){
		if(i!=0)ss<<BR;
		ss<< toString(map[i]);
	}
	return ss.str();
}

typedef int Cost;Cost CINF=1<<28;
namespace EGraph{
	struct Edge{
		int from,to;Cost cost;
		Edge(int from,int to,Cost cost)
		: from(from),to(to),cost(cost) {};
		bool operator<(Edge r) const{
			return cost<r.cost;
		}
		bool operator>(Edge r) const{
			return cost>r.cost;
		}
	};
	typedef vector<vector<Edge> >  Graph;
}
namespace MGraph{
	typedef  vector<vector<Cost> > Mat;
}
namespace ShortestPath{
    using namespace MGraph;
    // O(n^3) n≦100
    void warshall_floyd(Mat& d){
        const int V=d.size();
        REP(k,V)
            REP(i,V)REP(j,V){
                if(d[i][j]>d[i][k] + d[k][j]){
                    d[i][j]=d[i][k] + d[k][j];
                }
            }
    }
}
using namespace ShortestPath;
using namespace EGraph;

namespace MaximamFlows{
    typedef int Flow;
    const int INF = 1 << 28;
    struct Edge{
        int to;Flow cap;int rev;
        Edge(int to,Flow cap,int rev) : to(to),cap(cap),rev(rev) {};
    };
    typedef vector<vector<Edge> > Graph;

    //dinic O(V^2*E)
    class MaximamFlow{
    private:
           //iter　次に調べる時の開始位置 距離
        vector<int> iter,dist;
         //sからのbfs距離の計算
        void bfs_dist(int s){
            fill(ALL(dist),-1);dist[s]=0;
            queue<int> que;que.push(s);
            while(!que.empty()){
                int v=que.front();que.pop();
                EACH(e,G[v]){
                    if(e->cap>0 && dist[e->to] == -1){
                        dist[e->to]=dist[v]+1;
                        que.push(e->to);
                    }
                }
            }
        }
            //増加パス
        Flow dfs_best_path(int v,int t,Flow f){
            if(v==t)return f;
            for(int &i =iter[v];i<(int)G[v].size();i++){
                Edge& e=G[v][i];
                if(e.cap>0 && dist[v]<dist[e.to]){
                    Flow d=dfs_best_path(e.to,t,min(f,e.cap));
                    if(d>0){
                        e.cap-=d;G[e.to][e.rev].cap+=d;
                        return d;
                    }
                }
            }
            return 0;
        }
    public:
        int V;Graph G;
        MaximamFlow(int V):V(V){
            G=Graph(V);
            dist=vector<int>(V);iter=vector<int>(V);
        }

        void add_edge(int from,int to,int cap){
            int fromrev=G[to].size(),torev=G[from].size();
            G[from].push_back(Edge(to,cap,fromrev));G[to].push_back(Edge(from,0,torev));
        }
        int max_flow(int s,int t){
            Flow flow=0;
            while(true){
                bfs_dist(s);
                if(dist[t]<0)return flow;
                fill(ALL(iter),0);
                Flow f;
                while((f=dfs_best_path(s,t,INF))>0)flow+=f;
            }return -1;
        }
    };
}
using namespace MaximamFlows;

class Main{
public:
	int N,M,L;
	Mat g;
	vector<int> ps,ts;
	bool input(){
		nextInt(N);nextInt(M);nextInt(L);if(N==0)return false;
		g=Mat(N,vector<Cost>(N,CINF));
		REP(i,N)g[i][i]=0;
		REP(i,M){
			int u,v,d;nextInt(u);nextInt(v);nextInt(d);
			g[u][v]=g[v][u]=d;
		}
		ps=vector<int>(L);ts=vector<int>(L);
		REP(i,L){
			nextInt(ps[i]);nextInt(ts[i]);
		}
		return true;
	}

	void run(){
		while(input()){
			warshall_floyd(g);
			MaximamFlow mf(2*L+2);
			REP(i,L)REP(j,L)if(g[ps[i]][ps[j]]<=ts[j]-ts[i] &&i!=j){
				mf.add_edge(i, L+j,1);
			}
			REP(i,L)mf.add_edge(2*L,i,1);
			REP(j,L)mf.add_edge(L+j,2*L+1,1);

			cout <<L-mf.max_flow(2*L, 2*L+1)<<endl;
		}
	}
};

 int main(){
	//ios::sync_with_stdio(false);
 	Main().run();
 	return 0;
 }

Measured memory_bytes: 16836