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14D.go
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14D.go
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package main
import (
"bufio"
. "fmt"
"io"
)
// github.com/EndlessCheng/codeforces-go
func CF14D(_r io.Reader, out io.Writer) {
in := bufio.NewReader(_r)
var n, v, w, ans int
Fscan(in, &n)
g := make([][]int, n)
for i := 1; i < n; i++ {
Fscan(in, &v, &w)
v--
w--
g[v] = append(g[v], w)
g[w] = append(g[w], v)
}
d := func(u, no int) (maxD int) {
var f func(v, fa, d int)
f = func(v, fa, d int) {
if d > maxD {
maxD = d
u = v
}
for _, w := range g[v] {
if w != fa && w != no {
f(w, v, d+1)
}
}
}
maxD = -1
f(u, -1, 0)
maxD = -1
f(u, -1, 0)
return
}
var f func(v, fa int)
f = func(v, fa int) {
for _, w := range g[v] {
if w != fa {
if s := d(v, w) * d(w, v); s > ans {
ans = s
}
f(w, v)
}
}
}
f(0, -1)
Fprint(out, ans)
}
//func main() { CF14D(os.Stdin, os.Stdout) }