INF = float('inf')


class Dinic:
    class Edge:
        def __init__(self, to, cap, rev):
            self.to = to
            self.cap = cap
            self.rev = rev

    def __init__(self, V):
        self.V = V
        self.size = [0 for i in range(V)]
        self.G = [[] for i in range(V)]

    def add_edge(self, _from, to, cap):
        self.G[_from].append(Dinic.Edge(to, cap, self.size[to]))
        self.G[to].append(Dinic.Edge(_from, 0, self.size[_from]))
        self.size[_from] += 1
        self.size[to] += 1

    def bfs(self, s):
        from collections import deque

        level = [-1 for i in range(self.V)]
        level[s] = 0
        q = deque([s])
        while q:
            v = q.popleft()
            for u in self.G[v]:
                if u.cap > 0 and level[u.to] < 0:
                    level[u.to] = level[v] + 1
                    q.append(u.to)
        return level

    def dfs(self, v, t, f):
        if v == t: return f
        for i in range(self.iterator[v], self.size[v]):
            self.iterator[v] = i
            edge = self.G[v][i]
            if edge.cap > 0 and self.level[v] < self.level[edge.to]:
                d = self.dfs(edge.to, t, f if f < edge.cap else edge.cap)
                if d > 0:
                    self.G[v][i].cap -= d
                    self.G[edge.to][edge.rev].cap += d
                    return d
        return 0

    def max_flow(self, s, t):
        flow = 0
        while True:
            self.level = self.bfs(s)
            if self.level[t] < 0:
                return flow
            self.iterator = [0 for i in range(self.V)]
            while True:
                f = self.dfs(s, t, float('inf'))
                if f == 0:
                    break
                flow += f


def solve():
    N = int(input())
    mf = Dinic(N * 2 + 2)

    s = 0
    for i in range(N):
        b, c = list(map(int, input().split()))
        m = max(b, c)
        s += m
        mf.add_edge(0, i * 2 + 2, m - c)
        mf.add_edge(i * 2 + 2, i * 2 + 3, m)
        mf.add_edge(i * 2 + 3, 1, m - b)

    M = int(input())
    for i in range(M):
        d, e = list(map(int, input().split()))
        mf.add_edge(d * 2 + 3, e * 2 + 2, INF)

    print(s - mf.max_flow(0, 1))


if __name__ == '__main__':
    solve()