#include <bits/stdc++.h>
#define int long long
using namespace std;
const int MAXN = 100 + 3, INF = 1000 * 1000 * 1000 + 123, MAXK = 1000 + 23;
/*
4 5 2
10 9 5 2
-1 4 -1 15
-1 7 -1 9
-1 -1 -1 11
1 2 3
2 3 3
1 4 1
4 3 1
3 1 1
*/
int n, m, kk, d[MAXN][MAXN], b[MAXN][MAXK], s[MAXN][MAXK];
long double ans;
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr), cout.tie(nullptr);
cin >> n >> m >> kk;
for (int i = 0; i < n; i++){
for (int j = 0; j < n; j++){
if (i != j) d[i][j] = INF;
}
}
for (int i = 0; i < n; i++){
for (int j = 0; j < kk; j++){
cin >> b[i][j] >> s[i][j];
}
}
for (int i = 1; i < n; i++){
for(int j = 0; j < kk; j++){
if (b[i][j] != -1) return 0;
}
}
int v, w, t;
for (int i = 0; i < m; i++) {
cin >> v >> w >> t;
d[v--][w--] = t;
}
for (int k = 0; k < n; k++){
for(int i = 0; i < n; i++){
for(int j = 0; j < n; j++){
d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
}
}
}
for (int i = 1; i < n; i++) {
for(int j = 0; j < kk; j++){
if(~b[0][j] && ~s[i][j]) ans = max(ans, (long double)(s[i][j] - b[0][j]) / (d[0][i] + d[i][0]));
}
}
cout << (int)ans;
return 0;
}
