2
1 31
 2
1 0
 10
450661 128600 993228 725823 293549 33490 843121 903634 556169 448234
 1
1
 5
1 3 5 7 9
 6
524 529 5249 524 529 529
 3
1 2 3
 2
0 1
 55
0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 3 4 5 6 7 8 9 4 5 6 7 8 9 5 6 7 8 9 6 7 8 9 7 8 9 8 9 9
 16
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
 3
128 1024 2048
 10
3 3 3 5 5 3 3 3 3 5
 1
0
 2
1 2
 2
0 0
 2
1 1

0
 2
 632
 0
 0
 24
 2
 2
 621247139
 64594
 4
 0
 1
 1
 3
 0

#include <bits/stdc++.h>
#pragma GCC optimize("O2")
using namespace std;
inline long long input() {
  long long n;
  cin >> n;
  return n;
}
string base2(long long n) {
  string a = "";
  while (n >= 2) {
    a += (char)(n % 2 + '0');
    n /= 2;
  }
  a += (char)(n + '0');
  reverse((a).begin(), (a).end());
  return a;
}
const int MAXN = 1e6 + 10;
const int MOD = 1e9 + 7;
const int MOD2 = 998244353;
const long long INF = 8e18;
long long pw(long long a, long long b, long long mod) {
  return (!b ? 1
             : (b & 1 ? (a * pw(a * a % mod, b / 2, mod)) % mod
                      : pw(a * a % mod, b / 2, mod)));
}
vector<pair<long long, pair<long long, long long> > > G[MAXN];
long long E[MAXN], mark[MAXN], last[MAXN];
long long dis[MAXN];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  int n, m, k;
  cin >> n >> m >> k;
  for (int i = 1; i <= m; i++) {
    int a, b, c;
    cin >> a >> b >> c;
    G[a].push_back(make_pair(i, make_pair(b, c)));
    G[b].push_back(make_pair(i, make_pair(a, c)));
    E[i] = 0;
  }
  for (int i = 1; i <= k; i++) {
    int a = 1, b, c;
    cin >> b >> c;
    G[a].push_back(make_pair(i + m, make_pair(b, c)));
    G[b].push_back(make_pair(i + m, make_pair(a, c)));
    E[i + m] = 1;
  }
  for (int i = 1; i <= n; i++) {
    dis[i] = 1e18;
  }
  set<pair<long long, long long> > st;
  st.insert(make_pair(0ll, 1));
  dis[1] = 0;
  while (!st.empty()) {
    pair<long long, long long> cu = *st.begin();
    int v = cu.second;
    st.erase(st.begin());
    if (mark[v]) continue;
    mark[v] = 1;
    for (auto y : G[v]) {
      long long id = y.first, u = y.second.first, cost = y.second.second;
      if (dis[u] > dis[v] + cost) {
        dis[u] = dis[v] + cost;
        last[u] = E[id];
        st.insert(make_pair(dis[u], u));
      }
      if (dis[u] == dis[v] + cost && last[u] > E[id]) {
        last[u] = E[id];
      }
    }
  }
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    cnt += last[i];
  }
  cout << k - cnt;
  return 0;
}
