#include <iostream>
#include <cstdio>
#include <cassert>
#include <cstring>
#include <vector>
#include <valarray>
#include <array>
#include <queue>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <cmath>
#include <complex>
#include <random>

using namespace std;
typedef long long ll;

/**
 * Dinic?????????????????§???
 *
 * ?????¨???????????¬????????????
 * template?????°???int V???????????°
 */
const int INF = 1<<28;
template<int V>
struct MaxFlow {
    typedef int T;
    struct Edge {
        int to, rev;
        T cap;
    };
    vector<Edge> g[V];
    int level[V];
    int iter[V];
    /// ?????????
    void init() {
        for (int i = 0; i < V; i++) {
            g[i].clear();
        }
    }
    /// ??????????????????
    void add(int from, int to, T cap) {
        g[from].push_back(Edge{to, (int)g[to].size(), cap});
        g[to].push_back(Edge{from, (int)g[from].size()-1, 0});
    }
    /// ??????????????????
    void add_multi(int from, int to, T cap) {
        g[from].push_back(Edge{to, (int)g[to].size(), cap});
        g[to].push_back(Edge{from, (int)g[from].size()-1, cap});
    }

    void bfs(int s) {
        fill_n(level, V, -1);
        queue<int> que;
        level[s] = 0;
        que.push(s);
        while (!que.empty()) {
            int v = que.front(); que.pop();
            for (Edge e: g[v]) {
                if (e.cap <= 0) continue;
                if (level[e.to] < 0) {
                    level[e.to] = level[v] + 1;
                    que.push(e.to);
                }
            }
        }
    }

    T dfs(int v, int t, T 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) continue;
            if (level[v] < level[e.to]) {
                T d = dfs(e.to, t, min(f, e.cap));
                if (d <= 0) continue;
                e.cap -= d;
                g[e.to][e.rev].cap += d;
                return d;
            }
        }
        return 0;
    }

    // s??????t???????????§????????????
    T exec(int s, int t) {
        T flow = 0;
        while (true) {
            bfs(s);
            if (level[t] < 0) return flow;
            fill_n(iter, V, 0);
            T f;
            while ((f = dfs(s, t, INF)) > 0) {
                flow += f;
            }
        }
    }
};

typedef pair<int, int> P;
const int MN = 110;
const int ML = 1100;
MaxFlow<ML*2> mf;

int dist[MN][MN];
P qu[ML];
bool solve() {
    mf.init();
    int n, m, l;
    cin >> n >> m >> l;
    if (!n) return false;
    for (int i = 0; i < MN; i++) {
        for (int j = 0; j < MN; j++) {
            if (i == j) dist[i][j] = 0;
            else dist[i][j] = 1e8;
        }
    }
    for (int i = 0; i < m; i++) {
        int u, v, d;
        cin >> u >> v >> d;
        dist[u][v] = d;
        dist[v][u] = d;
    }
    for (int k = 0; k < n; k++) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                dist[i][j] = min(dist[i][j],
                    dist[i][k]+dist[k][j]);
            }
        }
    }


    for (int i = 0; i < l; i++) {
        int p, t;
        cin >> p >> t;
        qu[i] = P(t, p);
    }
    sort(qu, qu+l);

    int vs = 2*ML-1;
    int vt = 2*ML-2;
    for (int i = 0; i < l; i++) {
        for (int j = i+1; j < l; j++) {
            int ap, at, bp, bt;
            tie(at, ap) = qu[i];
            tie(bt, bp) = qu[j];
            if (dist[ap][bp] <= bt - at) {
                mf.add(i, j+ML, 1);
            }
        }
    }
    for (int i = 0; i < l; i++) {
        mf.add(vs, i, 1);
        mf.add(i+ML, vt, 1);
    }
    cout << l - mf.exec(vs, vt) << endl;
    return true;
}

int main() {
    while (true) {
        if (!solve()) break;
    }
    return 0;
}