#include<algorithm>
#include<bitset>
#include<cassert>
#include<cfloat>
#include<climits>
#include<cmath>
#include<deque>
#include<functional>
#include<iomanip>
#include<iostream>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<string>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>

using namespace std;

using lint = long long;
using P = pair<int, int>;
using LLP = pair<long long, long long>;

#define REP(i, x, n) for(int i = (x), i##_len = (int)(n) ; i < i##_len ; ++i)
#define rep(i, n) for(int i = 0, i##_len = (int)(n) ; i < i##_len ; ++i)
#define reps(i, n) for(int i = 1, i##_len = (int)(n) ; i <= i##_len ; ++i)
#define rrep(i, n) for(int i = (int)(n) - 1 ; i >= 0 ; --i)
#define rreps(i, n) for(int i = (int)(n) ; i > 0 ; --i)
#define SORT(x) sort((x).begin(), (x).end())
#define SORT_INV(x) sort((x).rbegin(), (x).rend())
#define REVERSE(x) reverse((x).begin(), (x).end())
#define TWINS(x) cout << ((x) ? "Yay!" : ":(") << '\n'
#define endl '\n'

constexpr int IINF = (1 << 30) - 1;
constexpr long long LLINF = 1LL << 61;
constexpr double EPS = 1e-10;

constexpr int dx4[] = {1, 0, -1, 0}, dy4[] = {0, 1, 0, -1};
constexpr int dx8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dy8[] = {0, -1, -1, -1, 0, 1, 1, 1};

template<typename T>
bool chmax(T& a, T b){
    if(a < b){
        a = b;
        return true;
    }
    return false;
}

template<typename T>
bool chmin(T& a, T b){
    if(b < a){
        a = b;
        return true;
    }
    return false;
}

struct BipartiteMatching {
  vector< vector< int > > graph;
  vector< int > match, alive, used;
  int timestamp;

  BipartiteMatching(int n) : graph(n), alive(n, 1), used(n, 0), match(n, -1), timestamp(0) {}

  void add_edge(int u, int v) {
    graph[u].push_back(v);
    graph[v].push_back(u);
  }

  bool dfs(int idx) {
    used[idx] = timestamp;
    for(auto &to : graph[idx]) {
      int to_match = match[to];
      if(alive[to] == 0) continue;
      if(to_match == -1 || (used[to_match] != timestamp && dfs(to_match))) {
        match[idx] = to;
        match[to] = idx;
        return true;
      }
    }
    return false;
  }

  int bipartite_matching() {
    int ret = 0;
    for(int i = 0; i < graph.size(); i++) {
      if(alive[i] == 0) continue;
      if(match[i] == -1) {
        ++timestamp;
        ret += dfs(i);
      }
    }
    return ret;
  }

  void output() {
    for(int i = 0; i < graph.size(); i++) {
      if(i < match[i]) {
        cout << i << "-" << match[i] << endl;
      }
    }
  }
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    int n, m, l;
    while(cin >> n >> m >> l, n){
        vector< vector<lint> > cost(n, vector<lint>(n, LLINF));
        rep(i, n){
            cost[i][i] = 0;
        }

        rep(i, m){
            int u, v;
            lint d;
            cin >> u >> v >> d;
            chmin(cost[u][v], d);
            chmin(cost[v][u], d);
        }

        rep(k, n){
            rep(i, n){
                rep(j, n){
                    chmin(cost[i][j], cost[i][k] + cost[k][j]);
                }
            }
        }

        vector<int> p(l);
        vector<lint> t(l);
        rep(i, l){
            cin >> p[i] >> t[i];
        }

        BipartiteMatching g(l << 1);

        rep(i, l){
            rep(j, i){
                if(abs(t[i] - t[j]) >= cost[p[i]][p[j]]){
                    if(t[i] < t[j]){
                        g.add_edge(i, j + l);
                    }else{
                        g.add_edge(j, i + l);
                    }
                }
            }
        }

        cout << l - g.bipartite_matching() << endl;
    }

    cout << flush;

    return 0;
}


Measured memory_bytes: 8168