class StronglyConnectedComponent:
    def __init__(self, N):
        self.N = N
        self.G = [[] for _ in range(N)]
        self.RevG = [[] for _ in range(N)]

    def AddEdge(self, u, v):
        self.G[u].append(v)
        self.RevG[v].append(u)

    def dfs(self, u):
        self.Used[u] = True
        for v in self.G[u]:
            if not self.Used[v]:
                self.dfs(v)
        self.PostOrder.append(u)

    def Revdfs(self, u):
        self.Group[u] = self.Lbcnt
        self.Used[u] = True
        for v in self.RevG[u]:
            if not self.Used[v]:
                self.Revdfs(v)

    def Build(self):
        self.PostOrder = []
        self.Used = [False] * self.N
        for i in range(self.N):
            if not self.Used[i]:
                self.dfs(i)
        self.Used = [False] * self.N
        self.Group = [None] * self.N
        self.Lbcnt = 0
        for i in reversed(self.PostOrder):
            if not self.Used[i]:
                self.Revdfs(i)
                self.Lbcnt += 1

    def Construct(self):
        DAG = [[] for _ in range(self.Lbcnt)]
        Groups = [[] for _ in range(self.Lbcnt)]
        for u in range(self.N):
            Lbu = self.Group[u]
            for v in self.G[u]:
                Lbv = self.Group[v]
                if Lbu == Lbv:
                    continue
                DAG[Lbu].append(Lbv)
            Groups[Lbu].append(u)
        return DAG, Groups

def dfs(u):
    flg[u] = True
    ret = 0
    for i in Groups[u]:
        ret += L[i] / 2
    for v in DAG[u]:
        ret += dfs(v)
    return ret

def MinCheck(u):
    ret = 1<<32
    for i in Groups[u]:
        ret = min(ret, L[i])
    return ret / 2

N = int(input())
Z = [list(map(int,input().split())) for _ in range(N)]
L,S = [list(i) for i in zip(*Z)]
SCC = StronglyConnectedComponent(N)
for i in range(N):
    SCC.AddEdge(S[i]-1, i)
SCC.Build()
DAG,Groups = SCC.Construct()
M = SCC.Lbcnt
flg = [False] * M
ans = 0
for i in range(M):
    if not flg[i]:
        ans += dfs(i)
        ans += MinCheck(i)
print(ans)