import sys
#sys.setrecursionlimit(n)
import heapq
import re
import bisect
import random
import math
import itertools
from collections import defaultdict, deque
from copy import deepcopy

n = int(input())
e = deque([[int(i) for i in input().split()] for i in range(n)])
e.appendleft([0,0])

v = [False] * (n + 1)
d = [False] * (n + 1)
def dfs(i, j):
  if d[e[i][1]]:
    return -1
  if i == j:
    return j
  if v[e[i][1]]:
    return -1
  v[i] = True
  ret = dfs(e[i][1], j)
  if ret == -1:
    return -1
  if e[i][0] < e[ret][0]:
    return i
  return ret

ans = 0
for i in range(1, n + 1):
  if d[i]:
    continue
  v = [False] * (n + 1)
  ret = dfs(e[i][1], i)
  if ret >= 0:
    ans += e[ret][0]
    d[ret] = True

for _ in range(1, n + 1):
  for i in range(1, n + 1):
    if d[e[i][1]] and not(d[i]):
      ans += e[i][0] / 2
      d[i] = True
print(ans)