// includes
#include <bits/stdc++.h>

// macros
#define ll long long int
#define pb emplace_back
#define mk make_pair
#define pq priority_queue
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define vrep(v, i) for(int i = 0; i < (v).size(); i++)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define FI first
#define SE second
#define dump(a, n) for(int i = 0; i < n; i++)cout << a[i] << "\n "[i + 1 != n];
#define dump2(a, n, m) for(int i = 0; i < n; i++)for(int j = 0; j < m; j++)cout << a[i][j] << "\n "[j + 1 != m];
#define bit(n) (1LL<<(n))
#define INT(n) int n; cin >> n;
#define LL(n) ll n; cin >> n;
#define DOUBLE(n) double n; cin >> n;
using namespace std;

//  types
typedef pair<int, int> P;
typedef pair<ll, int> Pl;
typedef pair<ll, ll> Pll;
typedef pair<double, double> Pd;
typedef complex<double> cd;
 
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

// solve
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << p.first << " " << p.second; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}

template <typename T>
struct edge {int to; T cap; int rev;};

template <typename T>
struct Graph{
  int n;
  vector<vector<edge<T>>> vec;
  vector<int> level;
  vector<int> iter;
  Graph(int n): n(n){
    vec.resize(n);
    level.resize(n);
    iter.resize(n);
  }
  void adde(int at, int to, T cap){
    vec[at].push_back((edge<T>){to, cap, (int)vec[to].size()});
    vec[to].push_back((edge<T>){at, 0, (int)vec[at].size() - 1});
  }
  void bfs(int s){
    fill(level.begin(), level.end(), -1);
    level[s] = 0;
    queue<int> q;
    q.push(s);
    while(!q.empty()){
      auto p = q.front(); q.pop();
      for(auto e: vec[p]){
        if(level[e.to] < 0 && e.cap > 0){
          level[e.to] = level[p] + 1;
          q.push(e.to);
        }
      }
    }
  }
  T dfs(int v, int t, T f){
    if(v == t)return f;
    int st = iter[v];
    for(int i = st; i < vec[v].size(); i++){
      iter[v] = i;
      auto& e = vec[v][i];
      if(level[v] < level[e.to] && e.cap > 0){
        auto d = dfs(e.to, t, min(f, e.cap));
        if(d > 0){
          e.cap -= d;
          vec[e.to][e.rev].cap += d;
          return d;
        }
      }
    }
    return 0;
  }
  T max_flow(int s, int t){
    T flow = 0;
    while(true){
      bfs(s);
      if(level[t] < 0)return flow;
      fill(iter.begin(), iter.end(), 0);
      T inf = numeric_limits<T>::max();
      T f = dfs(s, t, inf);
      while(f > 0){
        flow += f;
        f = dfs(s, t, inf);
      }
    }
  }
  T min_cut(int s, int t){
    return max_flow(s, t);
  }
};

using GraphI = Graph<int>;
using GraphL = Graph<long long>;

int main(int argc, char const* argv[])
{
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  // 0: source, 2*n+1: sink
  GraphL graph(2*n+2);
  ll res = 0;
  rep(i, n){
    int b, c;
    cin >> b >> c;
    res += b + c;
    graph.adde(0, i+1, b);
    graph.adde(i+1+n, 2*n+1, c);
    graph.adde(i+1,i+1+n, b + c);
  }
  INT(m);
  rep(i, m){
    int u, v;
    cin >> u >> v;
    graph.adde(u+1+n, v+1, inf);
  }
  cout << res - graph.min_cut(0, 2*n+1) << endl;
  return 0;
}