import collections


class DisjointSet(object):
    def __init__(self, n):
        self.parent = list(range(n))
        self.rank = [0] * n
        self.num = n  # number of disjoint sets

    def union(self, x, y):
        self._link(self.find_set(x), self.find_set(y))

    def _link(self, x, y):
        if x == y:
            return
        self.num -= 1
        if self.rank[x] > self.rank[y]:
            self.parent[y] = x
        else:
            self.parent[x] = y
            if self.rank[x] == self.rank[y]:
                self.rank[y] += 1

    def find_set(self, x):
        xp = self.parent[x]
        if xp != x:
            self.parent[x] = self.find_set(xp)
        return self.parent[x]


def read_data():
    N = int(input())
    Ls = []
    dst2src = []
    src2dst = [set() for n in range(N)]
    for n in range(N):
        l, s = map(int, input().split())
        Ls.append(l)
        dst2src.append(s - 1)
        src2dst[s - 1].add(n)
    return N, Ls, dst2src, src2dst


def solve(N, Ls, dst2src, src2dst):
    groups = decompose(N, dst2src)
    total = 0
    for group in groups:
        total += evaluate_difficulty(group, Ls, dst2src, src2dst)
    return total/2


def decompose(N, dst2src):
    djs = DisjointSet(N)
    for d, s in enumerate(dst2src):
        djs.union(d, s)
    groups = collections.defaultdict(set)
    for i in range(N):
        groups[djs.find_set(i)].add(i)
    return list(groups.values())


def evaluate_difficulty(group, Ls, dst2src, src2dst):
    score = sum(Ls[i] for i in group)
    trim_leaf(group, dst2src, src2dst)
    score += min(Ls[i] for i in group)
    return score
        
    
def trim_leaf(group, dst2src, src2dst):
    leaf = [i for i in group if not src2dst[i]]
    while leaf:
        dst = leaf[-1]
        del leaf[-1]
        group.remove(dst)
        src = dst2src[dst]
        src2dst[src].remove(dst)
        if not src2dst[src]:
            leaf.append(src)
    
if __name__ == '__main__':
    N, Ls, dst2src, src2dst = read_data()
    print('{:.1f}'.format(solve(N, Ls, dst2src, src2dst)))