#include <bits//stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef tree<long long, null_type, less<long long>, rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
typedef tree<long long, null_type, less_equal<long long>, rb_tree_tag,
tree_order_statistics_node_update>
ordered_multiset;
#define ll long long
#define ld long double
#define iloop(m, h) for (ll i = m; i != h; i += (m < h ? 1 : -1))
#define jloop(m, h) for (auto j = m; j != h; j += (m < h ? 1 : -1))
#define kloop(m, h) for (auto k = m; k != h; k += (m < h ? 1 : -1))
#define lloop(m, h) for (auto l = m; l != h; l += (m < h ? 1 : -1))
#define iloop_(m, h, g) for (auto i = m; i < h; i += g)
#define jloop_(m, h, g) for (auto j = m; j < h; j += g)
#define kloop_(m, h, g) for (auto k = m; k < h; k += g)
#define lloop_(m, h, g) for (auto l = m; l < h; l += g)
#define getchar_unlocked _getchar_nolock // comment before submission
#define pll pair<ll, ll>
#define plll pair<ll, pll>
#define pllll pair<pll, pll>
#define vll vector<ll>
#define qll queue<ll>
#define dll deque<ll>
#define pqll priority_queue<ll>
#define gll greater<ll>
#define INF 100000000000000
#define MOD1 1000000007
#define MOD2 998244353
#define MOD3 1000000009
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll n, m, t;
cin >> n >> m >> t;
ll a[n][t], b[n][t];
iloop(0, n) jloop(0, t) cin >> a[i][j] >> b[i][j];
ll t1, t2, t3;
ll dist[n][n];
iloop(0, n) jloop(0, n) dist[i][j] = INF;
//iloop(0, n) dist[i][i] = 0;
iloop(0, m) {
cin >> t1 >> t2 >> t3;
t1--, t2--;
dist[t1][t2] = min(dist[t1][t2], t3);
}
kloop(0, n) iloop(0, n) jloop(0, n) dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
//iloop(0, n) {jloop(0, n) {cout << dist[i][j] << " ";} cout << "\n";}
//cout << "\n";
ll opb[n][n];
iloop(0, n) jloop(0, n) opb[i][j] = 0;
iloop(0, n) jloop(0, n) kloop(0, t) if (a[i][k] != -1 && b[j][k] != -1) opb[i][j] = max(opb[i][j], b[j][k] - a[i][k]);
ll lb = 0, ub = 1e9, mid, adj[n][n];
while (lb < ub) {
mid = (lb + ub + 1) >> 1;
iloop(0, n) jloop(0, n) adj[i][j] = INF;
iloop(0, n) jloop(0, n) adj[i][j] = min(dist[i][j], INF / mid) * mid - opb[i][j];
//cout << mid << ":\n";
//iloop(0, n) {jloop(0, n) {cout << adj[i][j] << " ";} cout << "\n";}
//cout << "\n";
kloop(0, n) iloop(0, n) jloop(0, n) adj[i][j] = min(adj[i][j], adj[i][k] + adj[k][j]);
bool can = 0;
iloop(0, n) if (adj[i][i] <= 0) {can = 1; break;}
if (can) lb = mid;
else ub = mid - 1;
}
cout << lb;
}
