package main import ( "bufio" "fmt" "os" "sort" "strconv" ) func out(x ...interface{}) { fmt.Println(x...) } var sc = bufio.NewScanner(os.Stdin) func getInt() int { sc.Scan() i, e := strconv.Atoi(sc.Text()) if e != nil { panic(e) } return i } func getInts(N int) []int { ret := make([]int, N) for i := 0; i < N; i++ { ret[i] = getInt() } return ret } func getString() string { sc.Scan() return sc.Text() } // min, max, asub, absなど基本関数 func max(a, b int) int { if a > b { return a } return b } func min(a, b int) int { if a < b { return a } return b } func asub(a, b int) int { if a > b { return a - b } return b - a } func abs(a int) int { if a >= 0 { return a } return -a } func lowerBound(a []int, x int) int { idx := sort.Search(len(a), func(i int) bool { return a[i] >= x }) return idx } func upperBound(a []int, x int) int { idx := sort.Search(len(a), func(i int) bool { return a[i] > x }) return idx } var n int var l, s []int var done []int var used []int func rec(cur, tar int) (int, bool) { if done[s[cur]] == 1 { return -1, false } if cur == tar { return tar, true } if used[s[cur]] == 1 { return -1, false } used[cur] = 1 x, ok := rec(s[cur], tar) if !ok { return -1, false } if l[cur] < l[x] { return cur, true } return x, true } func main() { sc.Split(bufio.ScanWords) n = getInt() l = make([]int, n) s = make([]int, n) for i := 0; i < n; i++ { l[i], s[i] = getInt(), getInt()-1 l[i] *= 2 } done = make([]int, n) ans := 0 for i := 0; i < n; i++ { if done[i] == 0 { used = make([]int, n) x, ok := rec(s[i], i) if ok { ans += l[x] done[x] = 1 } } } for i := 0; i < n; i++ { for j := 0; j < n; j++ { if done[s[j]] == 1 && done[j] == 0 { done[j] = 1 ans += l[j] / 2 } } } fmt.Printf("%1.1f\n", (float64(ans) * 0.5)) }