#include<bits/stdc++.h>
using namespace std;
using Weight=long long;

struct Edge{
    int to;
    Weight cap,rev;
    Weight cost;
};

using Edges=vector<Edge>;
using Graph=vector<Edges>;

class Flow{
    const Weight INF=1e9+7;
    const bool isNegative=false;
    int N;
    Graph g;
    vector<int> level;
    vector<int> iter;
    void bfs(int s);
    Weight dfs(int v,int t,Weight f);
    public:
    Flow(int N):N(N),g(N){};
    void addEdge(int from,int to,Weight cap);
    void addEdge(int from,int to,Weight cap,Weight cost);
    Weight maxFlow(int s,int t);
    Weight minCostFlow(int s,int t,Weight f);
};


void Flow::addEdge(int from,int to,Weight cap){
    g[from].push_back({to,cap,int(g[to].size()),0});
    g[to].push_back({from,Weight(0),int(g[from].size())-1,0});
}

void Flow::addEdge(int from,int to,Weight cap,Weight cost){
    g[from].push_back({to,cap,int(g[to].size()),cost});
    g[to].push_back({from,Weight(0),int(g[from].size())-1,-cost});
}
Weight Flow::maxFlow(int s,int t){
    Weight flow=0;
    while(true){
        bfs(s);
        if(level[t]<0) return flow;
        iter.assign(N,0);
        Weight f;
        while((f=dfs(s,t,INF))>0){
            flow+=f;
        }
    }
}
void Flow::bfs(int s){
    level.assign(N,-1);
    queue<int> que;
    level[s]=0;
    que.push(s);
    while(!que.empty()){
        int v=que.front(); que.pop();
        for(int i=0;i<g[v].size();i++){
            Edge &e=g[v][i];
            if(e.cap>0 && level[e.to]<0){
                level[e.to]=level[v]+1;
                que.push(e.to);
            }
        }
    }
}

Weight Flow::dfs(int v,int t,Weight f){
    if(v==t) return f;
    for(int& i=iter[v];i<g[v].size();i++){
        Edge& e=g[v][i];
        if(e.cap>0 && level[v]<level[e.to]){
            Weight d=dfs(e.to,t,min(f,e.cap));
            if(d>0){
                e.cap-=d;
                g[e.to][e.rev].cap+=d;
                return d;
            }
        }
    }
    return 0;
}

Weight Flow::minCostFlow(int s,int t,Weight f){
    using P=pair<Weight,int>;
    Weight res=0;
    vector<Weight> h(N,0);
    vector<int> used(N),preve(N),prevv(N);
    vector<Weight> dist(N);
    while(f>0){    
        fill(dist.begin(),dist.end(),INF);
        dist[s]=0;
        if(!isNegative){
            //Dijkstra
            fill(used.begin(),used.end(),0);
            priority_queue<P,vector<P>,greater<P>> que;
            que.push(make_pair(Weight(0),s));
            while(!que.empty()){
                P p=que.top(); que.pop();
                int v=p.second;
                if(used[v]) continue;
                used[v]=true;
                for(int i=0;i<g[v].size();i++){
                    Edge &e=g[v][i];
                    if(e.cap>0 && dist[e.to]>dist[v]+e.cost+h[v]-h[e.to]){
                        dist[e.to]=dist[v]+e.cost+h[v]-h[e.to];
                        prevv[e.to]=v;
                        preve[e.to]=i;
                        que.push(make_pair(dist[e.to],e.to));
                    }
                }
            }
        }else{
            //Bermanford
            bool update=true;
            while(update){
                update=false;
                for(int v=0;v<N;v++){
                    if(dist[v]==INF) continue;
                    for(int i=0;i<g[v].size();i++){
                        Edge &e=g[v][i];
                        if(e.cap>0 && dist[e.to]>dist[v]+e.cost){
                            dist[e.to]=dist[v]+e.cost;
                            prevv[e.to]=v;
                            preve[e.to]=i;
                            update=true;
                        }
                    }
                }
            }
        }

        if(dist[t]==INF){
            return -1;
        }
        if(!isNegative){
            for(int v=0;v<N;v++) h[v]+=dist[v];
        }
        Weight d=f;
        for(int v=t;v!=s;v=prevv[v]){
            d=min(d,g[prevv[v]][preve[v]].cap);
        }
        f-=d;
        if(!isNegative){
            res+=d*h[t];
        }else{
            res+=d*dist[t];
        }
        for(int v=t;v!=s;v=prevv[v]){
            Edge& e=g[prevv[v]][preve[v]];
            e.cap-=d;
            g[v][e.rev].cap+=d;
        }
    }
    return res;
}

const int INF=1e9;
const int LSIZE=1000;
struct Query{
    int p,t;
};
bool operator<(Query lhs,Query rhs){
    return lhs.t<rhs.t;
}
int solve(int n,int m,int l){
    vector<vector<int>> d(n,vector<int>(n,INF));    
    for(int i=0;i<n;i++) d[i][i]=0;

    for(int i=0;i<m;i++){
        int u,v,tmp;
        cin>>u>>v>>tmp;
        d[u][v]=d[v][u]=tmp;
    }  
    vector<Query> q(l);
    for(int i=0;i<l;i++) cin>>q[i].p>>q[i].t;
    sort(q.begin(),q.end());
    
    for(int k=0;k<n;k++){
        for(int i=0;i<n;i++){
            for(int j=0;j<n;j++){
                d[i][j]=min(d[i][j],d[i][k]+d[k][j]);
            }
        }
    }
    using Bit=bitset<LSIZE>;
    vector<Bit> reachable(l);
    vector<pair<int,int>> dag;
    for(int i=l-1;i>=0;i--){
        for(int j=i+1;j<l;j++){
            if(reachable[i][j]) continue;
            if(q[j].t-q[i].t>=d[q[i].p][q[j].p]){
                reachable[i][j]=true;
                reachable[i]|=reachable[j];
                dag.push_back(make_pair(i,j));
            }
        }
    }

    Flow flow(2*l+4);
    const int S0=2*l;
    const int S1=2*l+1;
    const int T1=2*l+2;
    const int T0=2*l+3;
    auto in=[&](int x){return x;};
    auto out=[&](int x){return l+x;};

    const int A=0;
    const int B=1;
    const int C=10;
    flow.addEdge(S0,S1,n,0);
    flow.addEdge(T1,T0,n,0);
    for(int i=0;i<l;i++){
        flow.addEdge(S1,in(i),n,B);
    }
    flow.addEdge(S1,T1,n,A);
    for(auto e:dag){
        flow.addEdge(out(e.first),in(e.second),n,0);
    }
    for(int i=0;i<l;i++){
        flow.addEdge(in(i),out(i),n,0);
    }
    for(int i=0;i<l;i++){
        flow.addEdge(out(i),in(i),1,C);
        flow.addEdge(S0,out(i),1,0);
        flow.addEdge(in(i),T0,1,0);
    }
    for(int i=0;i<l;i++){
        flow.addEdge(out(i),T1,n,0);
    }
    int sumc=flow.minCostFlow(S0,T0,n+l);
    sumc-=C*l;
    int res=sumc+C*l-A*n;
    cout<<res<<endl;

    return 0;
}

int main(){
    int n,m,l;
    while(cin>>n>>m>>l,n){
        solve(n,m,l);
    }
    return 0;
}
