Problem:
Score : 400 points

Problem Statement

Takahashi will play a game using a piece on an array of squares numbered 1, 2, \cdots, N. Square i has an integer C_i written on it. Also, he is given a permutation of 1, 2, \cdots, N: P_1, P_2, \cdots, P_N.

Now, he will choose one square and place the piece on that square. Then, he will make the following move some number of times between 1 and K (inclusive):

In one move, if the piece is now on Square i (1 \leq i \leq N), move it to Square P_i. Here, his score increases by C_{P_i}.

Help him by finding the maximum possible score at the end of the game. (The score is 0 at the beginning of the game.)

Constraints

2 \leq N \leq 5000

1 \leq K \leq 10^9

1 \leq P_i \leq N

P_i \neq i

P_1, P_2, \cdots, P_N are all different.

-10^9 \leq C_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N K
P_1 P_2 \cdots P_N
C_1 C_2 \cdots C_N

Output

Print the maximum possible score at the end of the game.

Sample Input 1

5 2
2 4 5 1 3
3 4 -10 -8 8

Sample Output 1

8

When we start at some square of our choice and make at most two moves, we have the following options:

If we start at Square 1, making one move sends the piece to Square 2, after which the score is 4. Making another move sends the piece to Square 4, after which the score is 4 + (-8) = -4.

If we start at Square 2, making one move sends the piece to Square 4, after which the score is -8. Making another move sends the piece to Square 1, after which the score is -8 + 3 = -5.

If we start at Square 3, making one move sends the piece to Square 5, after which the score is 8. Making another move sends the piece to Square 3, after which the score is 8 + (-10) = -2.

If we start at Square 4, making one move sends the piece to Square 1, after which the score is 3. Making another move sends the piece to Square 2, after which the score is 3 + 4 = 7.

If we start at Square 5, making one move sends the piece to Square 3, after which the score is -10. Making another move sends the piece to Square 5, after which the score is -10 + 8 = -2.

The maximum score achieved is 8.

Sample Input 2

2 3
2 1
10 -7

Sample Output 2

13

Sample Input 3

3 3
3 1 2
-1000 -2000 -3000

Sample Output 3

-1000

We have to make at least one move.

Sample Input 4

10 58
9 1 6 7 8 4 3 2 10 5
695279662 988782657 -119067776 382975538 -151885171 -177220596 -169777795 37619092 389386780 980092719

Sample Output 4

29507023469

The absolute value of the answer may be enormous.

Solution in Rust (1.42.0) (judge verdict: Accepted)

#![allow(
  non_snake_case,
  unused_variables,
  unused_assignments,
  unused_mut,
  unused_imports,
  dead_code
)]
//use proconio::fastout;
use proconio::input;
use proconio::marker::*;
//use std::collections::HashSet;
use std::cmp::*;
use std::collections::*;
macro_rules! debug {
  ($($a:expr),* $(,)*) => {
      #[cfg(debug_assertions)]
      eprintln!(concat!($("| ", stringify!($a), "={:?} "),*, "|"), $(&$a),*);
  };
}
fn main() {
  input! {
     N:usize,
     K:usize,
     P:[Usize1;N],
     C:[i64;N]
  }
  // 各グループごとに
  // ・1周で稼げるスコア(どこから始めても同じ)と
  // ・各ポイントから各ポイントまで移動したときの最大得点
  // …を全部求め、移動回数K以下になるように実装する。
  // starts: グラフの始点を指すベクトル
  let mut starts = vec![N; N];
  let mut ans = std::i64::MIN;
  for i in 0..N {
    if starts[i] == N {
      starts[i] = i;
      let mut cycle_score = 0;
      let mut j = P[i];
      let mut s = vec![0; N * 2 + 1];
      let mut k = 0;
      s[k] = C[j];
      cycle_score += C[j];
      while starts[j] == N {
        starts[j] = i;
        j = P[j];
        k += 1;
        s[k] = C[j];
        cycle_score += C[j];
      }
      let cycle_len = k + 1;
      // 2周分のスコアを格納。
      for k in 0..cycle_len {
        s[cycle_len + k] = s[k];
      }
      let mut sum = vec![0; cycle_len * 2 + 1];
      for k in 0..cycle_len * 2 {
        sum[k + 1] = sum[k] + s[k];
      }
      // 1周分未満での最長スコアを計算(ただしK以下)
      // K以下の場合のtmaxと、K%cycle_len以下の場合のlmaxを計算。
      // 長さl以下の最高スコアsmax[l]を計算する。
      let mut smax = vec![std::i64::MIN; cycle_len];
      for len in 1..cycle_len {
        smax[len] = smax[len - 1];
        for l in 0..cycle_len {
          smax[len] = max(smax[len], sum[l + len] - sum[l]);
        }
      }
      // 周回スコア
      debug!(cycle_score, cycle_len);
      debug!(s);
      debug!(smax);
      let mut tmp = std::i64::MIN;
      if cycle_len > K {
        tmp = smax[K];
      } else if cycle_score < 0 {
        tmp = smax[cycle_len - 1];
      } else {
        tmp = cycle_score * ((K / cycle_len) as i64);
        for l in 1..min(K, cycle_len) {
          tmp = max(tmp, smax[l] + cycle_score * (((K - l) / cycle_len) as i64));
        }
      }
      ans = max(ans, tmp);
    }
  }
  println!("{}", ans);
}