#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<class t> using vc = vector<t>;
template<class t> using vvc = vc<vc<t>>;
using pi = pair<int,int>;
using pl = pair<ll,ll>;
using vi = vc<int>;
using vvi = vvc<int>;
using vl = vc<ll>;
using vvl = vvc<ll>;

#define rep(i,a,b) for (int i = (int)(a); i < (int)(b); i++)
#define irep(i,a,b) for (int i = (int)(a); i > (int)(b); i--)
#define all(a) a.begin(),a.end()
#define print(n) cout << n << '\n'
#define pritn(n) print(n)
#define printv(n,a) {copy(all(n),ostream_iterator<a>(cout," ")); cout<<"\n";}
#define printvv(n,a) {for(auto itr:n) printv(itr,a);}
#define rup(a,b) (a+b-1)/b
#define input(A,N) rep(i,0,N) cin>>A[i]
#define chmax(a,b) a = max(a,b)
#define chmin(a,b) a = min(a,b)

template< typename T >
struct edge{
    int from,to,rev;
    T cost;
    /*
    *to:繋がってる先
    *cost:辺のコスト
    */
    edge(int from,int to,int rev,T cost):from(from),to(to),rev(rev),cost(cost){};
    edge &operator=(const int& x){
        to = x;
        return *this;
    }
};

template< typename T >
struct graph{
    int n;
    vector<vector<edge<T>>> e;
    graph(int n):n(n),e(n){}

    void addedge(int from,int to,T cost){
        e[from].emplace_back(from,to,(int)e[to].size(),cost);
        e[to].emplace_back(to,from,(int)e[from].size()-1,0);
    }

    vector<edge<T>> &operator[](int i) {
        return e[i];
    }
};

template< typename T >
struct FordFulkerson{
    const int INF = (T)1e9;
    vector<int> vis;

    FordFulkerson(){};

    T dfs(graph<T>&g,int ni,int t,T f){
        if(ni==t) return f;
        vis[ni] = 1;
        for(auto &e:g[ni]){
            if(vis[e.to]||e.cost<=0) continue;
            T d = dfs(g,e.to,t,min(f,e.cost));
            if(d>0){
                e.cost -= d;
                g[e.to][e.rev].cost += d;
                return d;
            }
        }
        return 0;
    }

    //start:s->to:t
    T max_flow(graph<T>&g,int s,int t){
        T flow = 0;
        while(1){
            vis.assign(g.n,0);
            T d = dfs(g,s,t,INF);
            if(d==0){
                return flow;
            }else{
                flow += d;
            }
        }
        return 0;
    }
};


int main(){
    cout << fixed << setprecision(15);
    
    int n;
    cin>>n;
    graph<int> g(n+2);
    int now = 0;
    rep(i,0,n){
        int b,c;
        cin>>b>>c;
        if(b>c){
            now += b;
            b -= c;
            g.addedge(i,n+1,b);
        }else{
            now += c;
            c -= b;
            g.addedge(n,i,c);
        }
    }
    int m;
    cin>>m;
    int inf = (int)1e9;
    rep(i,0,m){
        int a,b;
        cin>>a>>b;
        g.addedge(b,a,inf);
    }
    FordFulkerson<int> f;
    print(now-f.max_flow(g,n,n+1));

    //system("pause");
    return 0;
}