#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  ll gain = 0;
  int s = n, t = n + 1;
  mf_graph<int> g(t + 1);
  rep(i, n) {
    int a, b;
    cin >> a >> b;
    if (a > b) {
      gain += a;
      g.add_edge(s, i, a - b);
    } else {
      gain += b;
      g.add_edge(i, t, b - a);
    }
  }
  rep(_, m) {
    int u, v, c;
    cin >> u >> v >> c;
    u--, v--;
    g.add_edge(u, v, c);
    g.add_edge(v, u, c);
  }
  cout << gain - g.flow(s, t) << '\n';
}