fn main() {
    input! {
        n: usize,
        w: usize,
        p: [usize1; n - 1],
        item: [(i64, usize); n - 1],
    }
    let mut child = vec![vec![]; n];
    for (i, p) in p.iter().enumerate() {
        child[*p].push(i + 1);
    }
    let mut item = item;
    item.insert(0, (0, 0));
    let inf = std::i64::MAX / 2;
    let mut ini = vec![inf; w + 1];
    ini[0] = 0;
    let ans = recurse(|rec, (v, mut dp): (usize, Vec<i64>)| -> Vec<i64> {
        let (c, s) = item[v];
        for dp in dp.iter_mut() {
            *dp += c;
        }
        dp.resize(w + 1 + s, inf);
        dp.rotate_right(s);
        dp[w] = *dp[w..].iter().min().unwrap();
        dp.truncate(w + 1);
        for &u in child[v].iter() {
            let c = rec((u, dp.clone()));
            for (dp, c) in dp.iter_mut().zip(c.iter()) {
                if *dp > *c {
                    *dp = *c;
                }
            }
        }
        dp
    })((0, ini));
    println!("{}", ans[w]);
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------
// ---------- begin recurse ----------
// reference
// https://twitter.com/noshi91/status/1393952665566994434
// https://twitter.com/shino16_cp/status/1393933468082397190
pub fn recurse<A, R, F>(f: F) -> impl Fn(A) -> R
where
    F: Fn(&dyn Fn(A) -> R, A) -> R,
{
    fn call<A, R, F>(f: &F, a: A) -> R
    where
        F: Fn(&dyn Fn(A) -> R, A) -> R,
    {
        f(&|a| call(f, a), a)
    }
    move |a| call(&f, a)
}
// ---------- end recurse ----------