#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<to;x++)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

template<class V> class MaxFlow_dinic {
public:
	struct edge { int to,reve;V cap;};
	static const int MV = 1100;
	vector<edge> E[MV];
	int itr[MV],lev[MV];
	
	void add_edge(int x,int y,V cap) {
		E[x].push_back((edge){y,(int)E[y].size(),cap});
		E[y].push_back((edge){x,(int)E[x].size()-1,0}); // directed
		//E[y].push_back((edge){x,(int)E[x].size()-1,cap}); // undirect
	}
	
	void bfs(int cur) {
		MINUS(lev);
		queue<int> q;
		lev[cur]=0;
		q.push(cur);
		while(q.size()) {
			int v=q.front(); q.pop();
			ITR(e,E[v]) if(e->cap>0 && lev[e->to]<0) lev[e->to]=lev[v]+1, q.push(e->to);
		}
	}
	
	int dfs(int from,int to,V cf) {
		if(from==to) return cf;
		ITR(e,E[from]) if(e->cap>0 && lev[from]<lev[e->to]) {
			V f=dfs(e->to,to,min(cf,e->cap));
			if(f>0) {
				e->cap-=f;
				E[e->to][e->reve].cap += f;
				return f;
			}
		}
		return 0;
	}
	
	V maxflow(int from, int to) {
		V fl=0,tf;
		while(1) {
			bfs(from);
			if(lev[to]<0) return fl;
			ZERO(itr);
			while((tf=dfs(from,to,numeric_limits<V>::max()))>0) fl+=tf;
		}
	}
};

int N,M;
int B[101],C[101];

MaxFlow_dinic<int> mf;
int mat[101][101];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	int tot=0;
	FOR(i,N) {
		cin>>B[i]>>C[i];
		tot+=B[i]+C[i];
		mf.add_edge(0,1+i,B[i]);
		mf.add_edge(100+i,200,C[i]);
		mf.add_edge(1+i,100+i,10000);
	}
	cin>>M;
	FOR(i,M) {
		cin>>x>>y;
		mf.add_edge(1+x,100+y,10000);
	}
	cout<<tot-mf.maxflow(0,200)<<endl;
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false);
	FOR(i,argc-1) s+=argv[i+1],s+='\n';
	FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	solve(); return 0;
}