n = int(input())
l, s = [], []
ans = 0
for _ in range(n):
    li, si = map(int, input().split())
    l.append(li)
    s.append(si - 1)
    ans += li
visited = [False] * n
for i in range(n):
    if visited[i]:
        continue
    seq = []
    while not visited[i]:
        visited[i] = True
        seq.append(i)
        i = s[i]
    if i not in seq:
        continue
    ans += min(l[j] for j in seq[seq.index(i):])
print(ans / 2)