package main import ( "bufio" "fmt" "os" "strconv" ) func getScanner(fp *os.File) *bufio.Scanner { scanner := bufio.NewScanner(fp) scanner.Split(bufio.ScanWords) scanner.Buffer(make([]byte, 1000005), 1000005) return scanner } func getNextString(scanner *bufio.Scanner) string { scanner.Scan() return scanner.Text() } func getNextInt(scanner *bufio.Scanner) int { i, _ := strconv.Atoi(getNextString(scanner)) return i } func getNextInt64(scanner *bufio.Scanner) int64 { i, _ := strconv.ParseInt(getNextString(scanner), 10, 64) return i } func getNextUint64(scanner *bufio.Scanner) uint64 { i, _ := strconv.ParseUint(getNextString(scanner), 10, 64) return i } func getNextFloat64(scanner *bufio.Scanner) float64 { i, _ := strconv.ParseFloat(getNextString(scanner), 64) return i } func main() { fp := os.Stdin wfp := os.Stdout cnt := 0 if os.Getenv("MASPY") == "ますピ" { fp, _ = os.Open(os.Getenv("BEET_THE_HARMONY_OF_PERFECT")) cnt = 1 } if os.Getenv("MASPYPY") == "ますピッピ" { wfp, _ = os.Create(os.Getenv("NGTKANA_IS_GENIUS10")) } scanner := getScanner(fp) writer := bufio.NewWriter(wfp) solve(scanner, writer) for i := 0; i < cnt; i++ { fmt.Fprintln(writer, "-----------------------------------") solve(scanner, writer) } writer.Flush() } func solve(scanner *bufio.Scanner, writer *bufio.Writer) { n := getNextInt(scanner) g := newGraph(n) for i := 0; i < n-1; i++ { u := getNextInt(scanner) - 1 v := getNextInt(scanner) - 1 w := getNextInt(scanner) g.appendEdge(u, v, i, w) g.appendEdge(v, u, i, w) } g.dfs(0, -1) fmt.Fprintln(writer, g.ans*2) } type graph struct { v []vertex e [][]edge ans int64 } func newGraph(n int) *graph { return &graph{ v: make([]vertex, n), e: make([][]edge, n), } } func (g *graph) dfs(c, p int) int { cnt := 1 for _, e := range g.e[c] { if e.to == p { continue } ch := g.dfs(e.to, c) cnt += ch g.ans += int64(ch) * int64(len(g.v)-ch) * int64(e.w) } return cnt } func (g *graph) appendEdge(from, to, id, w int) { g.e[from] = append(g.e[from], edge{ to: to, id: id, w: w, }) } type vertex struct { } type edge struct { to, id, w int }