from collections import deque
# from math import inf
from typing import List, Tuple, Union
import sys
sys.setrecursionlimit(10**6)

inf = 10**9


class MaxFlow:

    def __init__(self, N: int):
        self.__N: int = N
        self.__G: List[List[MaxFlow.Edge]] = [[] for _ in range(N)]
        self.__E: List[Tuple[MaxFlow.Edge, MaxFlow.Edge]] = []

    def add_edge(self, from_: int, to: int, capacity: Union[int, float]):
        assert 0 <= from_ < self.__N
        assert 0 <= to < self.__N
        assert 0 <= capacity

        from_edge = [to, None, capacity]
        to_edge = [from_, from_edge, 0]
        from_edge[1] = to_edge

        self.__E.append((from_edge, to_edge))
        self.__G[from_].append(from_edge)
        self.__G[to].append(to_edge)

        return len(self.__E) - 1

    def flow(self, source: int, sink: int,
             flow_limit: Union[int, float] = inf):
        assert 0 <= source < self.__N
        assert 0 <= sink < self.__N
        assert source != sink
        assert flow_limit >= 0

        level: List[int] = []
        cnt: List[int] = []

        def bfs():
            level[source] = 0
            Q = deque([source])
            while len(Q) != 0:
                u = Q.popleft()
                for edg in self.__G[u]:
                    to, _, cap = edg
                    if cap > 0 and level[to] == -1:
                        level[to] = level[u] + 1
                        if to == sink:
                            return True
                        Q.append(to)
            return False

        def flow(e, f):
            if e == sink:
                return f

            while cnt[e] < len(self.__G[e]):
                edg = self.__G[e][cnt[e]]
                to, rev, cap = edg

                if cap <= 0 or level[to] <= level[e]:
                    cnt[e] += 1
                    continue

                flowed = flow(to, min(f, cap))
                if flowed > 0:
                    edg[2] -= flowed
                    rev[2] += flowed
                    return flowed

            level[e] = -1
            return 0

        answer = 0
        while flow_limit > 0:
            level = [-1] * self.__N
            cnt = [0] * self.__N

            if not bfs():
                break

            while True:
                flowed = flow(source, flow_limit)
                if flowed <= 0:
                    break

                answer += flowed
                flow_limit -= flowed

        return answer


def main():
    N = int(input())
    BC = [tuple(map(int, input().split())) for i in range(N)]
    M = int(input())
    DE = [tuple(map(int, input().split())) for i in range(M)]

    G = MaxFlow(2*N+2)
    ans = 0
    for i in range(N):
        B, C = BC[i]
        ans += max(B, C)
        G.add_edge(2*N, 2*i, max(B, C) - C)
        G.add_edge(2*i, 2*i+1, max(B, C))
        G.add_edge(2*i+1, 2*N+1, max(B, C) - B)

    for d, e in DE:
        G.add_edge(2*d+1, 2*e, inf)

    ans -= G.flow(2*N, 2*N+1)

    print(ans)


if __name__ == '__main__':
    main()