#include <bits/stdc++.h>

using namespace std;

const int mod = 1000000007;

int modmul(int64_t a, int64_t b) {
    return static_cast<int>(a * b % mod);
}

int modpow(int e, int p) {
    int r = 1;
    while (p) {
        if (p & 1) r = modmul(r, e);
        e = modmul(e, e);
        p >>= 1;
    }
    return r;
}

int modpow(int64_t e, int p, int m) {
    int64_t r = 1;
    while (p) {
        if (p & 1) r = r * e % m;
        e = e * e % m;
        p >>= 1;
    }
    return r;
}

signed main() {
    cin.tie(nullptr) -> sync_with_stdio(false);
    int N, K;
    cin >> N >> K;
    vector<int> P(N);
    vector<vector<int>> G(N);
    for (int i = 1; i < N; i++) {
        cin >> P[i];
        --P[i];
        G[P[i]].emplace_back(i);
    }

    vector<int> E(N);
    const int nk = modpow(N, K);
    for (int i = 0; i < N; i++) {
        cin >> E[i];
        E[i] = modmul(E[i], nk);
    }

    for (int i = N - 1; i >= 1; i--) {
        E[P[i]] = (E[P[i]] + E[i]) % mod;
    }

    const int mod2 = (mod - 1) / 2;

    if (K == mod2) {
        for (int i = 0; i < N; i++) {
            if (E[i] != 0 && E[i] != 1 && E[i] != mod-1) {
                cout << -1 << '\n';
                return 0;
            }
        }
        int x = 0;
        int y = 0;
        if (E[0] == 0) ;
        else if (E[0] == 1) ++x;
        else ++y;

        for (int i: G[0]) {
            if (E[i] == 0) ;
            else if (E[i] == 1) ++y;
            else ++x;
        }

        if (y == 0 && (x == 1 || x == 2)) {
            cout << 1 << '\n';
        } else if (y == 2 && x == 0) {
            cout << 1 << '\n';
        } else if (y == 1 && x == 0) {
            int Z = 1;
            while (modpow(Z, (mod - 1) / 2) == 1)
                ++Z;
            cout << Z << '\n';
        } else {
            cout << 0 << '\n';
        }

    } else {
        const int invK = modpow(K, mod2 - 2, mod - 1);
        // cerr << "here " << invK * K % mod2 << endl;
        // cerr << "===" << endl;
        // for (int i = 0; i < N; i++) {
        //     cerr << modpow(E[i], invK) << endl;
        // }
        // cerr << "===" << endl;

        int ans = modpow(E[0], invK);
        for (int i: G[0]) {
            ans = (ans - modpow(E[i], invK) + mod) % mod;
        }
        cout << ans << '\n';
    }
}