#include <bits/stdc++.h>
 
using namespace std;
#define int long long
const int mx = 112;
typedef pair<int, int> ii;
vector<int> adj[mx];
int A[mx], B[mx], n;

bool check (int hp) {
  vector<bool> inq(mx, 0);
  priority_queue<ii> pq;
  pq.emplace(0, 0);
  while (!pq.empty()) {
    auto[w, v] = pq.top();
    inq[v] = true;
    hp += w;
    pq.pop();
    for (int i = 0; i < n; i++) {
      if (inq[i]) {
        for (auto u : adj[i]) {
          if (!inq[u] && A[u] <= hp) {
            pq.emplace(B[u] - A[u], u);
          }
        }
      }
    }
  }
  for (int i = 0; i < n; i++) {
    if (!inq[i]) return 0;
  }
  return 1;
}

int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int m;
  cin >> n >> m;
  for (int i = 1; i < n; i++) {
    cin >> A[i] >> B[i];
  }
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--, b--;
    adj[a].emplace_back(b);
  }
  int lo = 0, hi = 1e18;
  while (hi - lo > 1) {
    int mid = (lo+hi)/2;
    if (check(mid)) hi = mid;
    else lo = mid;
  }
  if (hi < lo) swap(lo, hi);
  if (check(lo)) cout << lo << endl;
  else cout << hi << endl;
}