#include <bits/stdc++.h>
using namespace std;
#define int long long int
const int INF = 1e18 + 10;
const int MAXN = 1e3 + 10;
int B[MAXN][MAXN];
int S[MAXN][MAXN];
int dist[MAXN][MAXN];
signed main()
{
int n, m, k, ans = 0;
cin >> n >> m >> k;
for (int i = 1; i <= n; i++)
{
for (int j = 1; j <= n; j++)
{
dist[i][j] = INF;
}
}
for (int i = 1; i <= n; i++)
{
for (int j = 1; j <= k; j++)
{
cin >> B[i][j] >> S[i][j];
}
}
for (int i = 1; i <= m; i++)
{
int v, u, w;
cin >> v >> u >> w;
dist[v][u] = min(dist[v][u], w);
}
for (int k = 1; k <= n; k++)
{
for (int i = 1; i <= n; i++)
{
for (int j = 1; j <= n; j++)
{
dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
}
}
}
for (int i = 1; i <= k; i++)
{
for (int j = 1; j <= n; j++)
{
if (B[1][i] == -1 || S[j][i] == -1 || dist[1][j] == INF || dist[j][1] == INF)
continue;
int t = dist[1][j] + dist[j][1];
int val = S[j][i] - B[1][i];
ans = max(ans, val / t);
}
}
cout << ans << endl;
return 0;
}
