n = int(input())
g = [0]*n
diff = [0]*n
for i in range(n):
    diff[i],s = map(int,input().split())
    g[i] = s-1
ans = sum(diff)
used = [0]*n
for i in range(n):
    if used[i]: continue
    lst = []
    while used[i]==0:
        used[i] = 1
        lst.append(i)
        i = g[i]
    if i in lst:
        ans += min(diff[k] for k in lst[lst.index(i):])
print(ans/2)