#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <functional>
#include <cassert>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
#define whole(f,x,...) ([&](decltype((x)) y) { return (f)(begin(y), end(y), ## __VA_ARGS__); })(x)
template <class T> bool setmin(T & l, T const & r) { if (not (r < l)) return false; l = r; return true; }
using namespace std;

struct edge_t { int to, cap, rev; };
int maximum_flow_destructive(int s, int t, vector<vector<edge_t> > & g) {
    int n = g.size();
    vector<bool> used(n);
    function<int (int, int)> dfs = [&](int i, int f) {
        if (i == t) return f;
        used[i] = true;
        for (edge_t & e : g[i]) {
            if (used[e.to] or e.cap <= 0) continue;
            int nf = dfs(e.to, min(f, e.cap));
            if (nf > 0) {
                e.cap -= nf;
                g[e.to][e.rev].cap += nf;
                return nf;
            }
        }
        return 0;
    };
    int result = 0;
    while (true) {
        used.clear(); used.resize(n);
        int f = dfs(s, numeric_limits<int>::max());
        if (f == 0) break;
        result += f;
    }
    return result;
}

vector<pair<int,int> > perfect_bipartite_matching(set<int> const & a, set<int> const & b, vector<vector<int> > const & g /* adjacency list */) { // O(V + FE)
    assert (a.size() + b.size() <= g.size());
    int n = g.size();
    int src = n;
    int dst = n + 1;
    vector<vector<edge_t> > h(n + 2);
    auto add_edge = [&](int from, int to, int cap) {
        h[from].push_back((edge_t) {   to, cap, int(h[  to].size()    ) });
        h[  to].push_back((edge_t) { from,   0, int(h[from].size() - 1) });
    };
    repeat (i,n) {
        if (a.count(i)) {
            add_edge(src, i, 1);
            for (int j : g[i]) if (b.count(j)) {
                add_edge(i, j, 1); // collect edges e : a -> b, from g
            }
        }
        if (b.count(i)) {
            add_edge(i, dst, 1);
        }
    }
    maximum_flow_destructive(src, dst, h);
    vector<pair<int,int> > ans;
    for (int from : a) {
        for (edge_t e : h[from]) if (b.count(e.to) and e.cap == 0) {
            ans.emplace_back(from, e.to);
        }
    }
    return ans;
}

const int inf = 1e9+7;
int main() {
    while (true) {
        // input
        int n, m, l; cin >> n >> m >> l;
        if (n == 0 and m == 0 and l == 0) break;
        vector<map<int,int> > g(n);
        repeat (i,m) {
            int u, v, d; cin >> u >> v >> d;
            g[u][v] = d;
            g[v][u] = d;
        }
        vector<int> p(l), t(l);
        repeat (i,l) cin >> p[i] >> t[i];
        // warshall floyd
        vector<vector<int> > dist(n, vector<int>(n, inf));
        repeat (i,n) dist[i][i] = 0;
        repeat (i,n) for (auto it : g[i]) dist[i][it.first] = it.second;
        repeat (k,n) repeat (i,n) repeat (j,n) setmin(dist[i][j], dist[i][k] + dist[k][j]);
        // make a digraph of presents, DAG
        vector<vector<int> > h(2*l);
        repeat (i,l) repeat (j,l) if (i != j) if (dist[p[i]][p[j]] <= t[j] - t[i]) h[i].push_back(j + l);
        // let it flow
        set<int> a, b;
        repeat (i,l) a.insert(i);
        repeat (j,l) b.insert(j + l);
        auto move = perfect_bipartite_matching(a, b, h);
        // output
        cout << l - move.size() << endl;
    }
    return 0;
}

Measured memory_bytes: 21540