#include <bits/stdc++.h>
using namespace std;

#define int long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define reps(i, n) for (int i = 1; i <= (n); i++)
#define all(x) (x).begin(), (x).end()
#define uniq(x) (x).erase(unique(all(x)), end(x))
#define bit(n) (1LL << (n))
#define cdiv(a, b) (((a) - 1) / (b) + 1)
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template<typename T> using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.1415926535897932384626433832795028;
constexpr int DY[8] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr int DX[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int gcd(int a, int b) {
    while (b) { swap(a %= b, b); }
    return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
template<typename T> void fin(T mes) {
    cout << mes << endl;
    exit(0);
}
template<typename T, typename U> bool chmax(T &a, const U &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> bool chmin(T &a, const U &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
    os << "(" << rhs.first << ", " << rhs.second << ")";
    return os;
}
template<typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
    os << "{";
    for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
        os << *itr << (next(itr) != rhs.end() ? ", " : "");
    }
    os << "}";
    return os;
}
struct setup {
    static constexpr int PREC = 20;
    setup() {
        cout << fixed << setprecision(PREC);
        cerr << fixed << setprecision(PREC);
    };
} setup;

struct union_find_tree {
    std::vector<int> par, size;
    union_find_tree(int n) : par(n), size(n) {
        for (int i = 0; i < n; i++) {
            par[i] = i;
            size[i] = 1;
        }
    }
    int get_root(int i) {
        if (par[i] == i) { return i; }
        else { return par[i] = get_root(par[i]); }
    }
    void unite(int i, int j) {
        if ((i = get_root(i)) == (j = get_root(j))) { return; }
        if (size[i] < size[j]) { std::swap(i, j); }
        par[j] = i;
        size[i] += size[j];
    }
    bool are_same(int i, int j) { return get_root(i) == get_root(j); }
    int get_size(int i) { return size[get_root(i)]; }
};

template<int MOD = 1000000007>
struct mod_int {
    int val;
    mod_int(long long val_ = 0) : val(val_ % MOD) { if (val < 0) { val += MOD; }}
    bool operator==(const mod_int &rhs) const { return val == rhs.val; }
    bool operator!=(const mod_int &rhs) const { return std::rel_ops::operator!=(*this, rhs); }
    mod_int &operator+=(const mod_int &rhs) {
        if ((val += rhs.val) >= MOD) { val -= MOD; }
        return *this;
    }
    mod_int &operator-=(const mod_int &rhs) {
        if ((val += MOD - rhs.val) >= MOD) { val -= MOD; }
        return *this;
    }
    mod_int &operator*=(const mod_int &rhs) {
        val = (int) ((long long) val * rhs.val % MOD);
        return *this;
    }
    mod_int &operator/=(const mod_int &rhs) { return *this *= rhs.inv(); }
    mod_int operator+() const { return *this; }
    mod_int operator-() const { return -val; }
    mod_int operator++() { return *this += 1; }
    mod_int operator--() { return *this -= 1; }
    mod_int operator++(signed) {
        const mod_int ret(*this);
        ++*this;
        return ret;
    }
    mod_int operator--(signed) {
        const mod_int ret(*this);
        --*this;
        return ret;
    }
    mod_int operator+(const mod_int &rhs) const { return mod_int(*this) += rhs; }
    mod_int operator-(const mod_int &rhs) const { return mod_int(*this) -= rhs; }
    mod_int operator*(const mod_int &rhs) const { return mod_int(*this) *= rhs; }
    mod_int operator/(const mod_int &rhs) const { return mod_int(*this) /= rhs; }
    mod_int inv() const {
        assert(val != 0);
        int a = val, b = MOD, x = 1, u = 0;
        while (b) {
            int t = a / b;
            std::swap(a -= t * b, b);
            std::swap(x -= t * u, u);
        }
        return x;
    }
    mod_int pow(long long n) const {
        if (n < 0) { return pow(-n).inv(); }
        mod_int ret = 1, mul = *this;
        while (n) {
            if (n & 1) { ret *= mul; }
            mul *= mul;
            n >>= 1;
        }
        return ret;
    }
    friend std::istream &operator>>(std::istream &is, mod_int &rhs) {
        long long v;
        is >> v;
        rhs = v;
        return is;
    }
    friend std::ostream &operator<<(std::ostream &os, const mod_int &rhs) { return os << rhs.val; }
    struct combination {
        std::vector<mod_int> fact{1, 1}, f_inv{1, 1}, inv{0, 1};
        void calc(int n) {
            while (fact.size() <= n) {
                int i = fact.size();
                fact.push_back(fact[i - 1] * i);
                inv.push_back(-inv[MOD % i] * (MOD / i));
                f_inv.push_back(f_inv[i - 1] * inv[i]);
            }
        }
        mod_int P(int n, int r) { return r < 0 || n < r ? 0 : (calc(n), fact[n] * f_inv[n - r]); }
        mod_int C(int n, int r) { return r < 0 || n < r ? 0 : (calc(n), fact[n] * f_inv[r] * f_inv[n - r]); }
        mod_int H(int n, int r) { return C(n + r - 1, r); }
    };
};

using mint = mod_int<>;
signed main() {
    int N;
    cin >> N;
    vint P(N);
    union_find_tree uf(N);
    vint yet;
    int R = N;
    rep(i, N) {
        cin >> P[i];
        if (P[i] == -1) { yet.push_back(i); }
        else {
            P[i]--;
            if (!uf.are_same(i, P[i])) {
                uf.unite(i, P[i]);
                R--;
            }
        }
    }
    int K = yet.size();
    mint ans = mint(N) * mint(N - 1).pow(K);
    ans -= mint(R - K) * mint(N - 1).pow(K);
    rep(i, K) { ans -= mint(N - 1).pow(K - 1) * (uf.get_size(yet[i]) - 1); }
    vector<vector<mint>> dp(K + 1, vector<mint>(K + 1));
    dp[0][0] = 1;
    rep(i, K) {
        rep(j, K) {
            dp[i + 1][j] += dp[i][j];
            dp[i + 1][j + 1] += dp[i][j] * uf.get_size(yet[i]);
        }
    }
    mint::combination comb;
    comb.calc(K);
    for (int i = 2; i <= K; i++) { ans -= mint(N - 1).pow(K - i) * comb.fact[i - 1] * dp[K][i]; }
    cout << ans << endl;
}

Measured memory_bytes: 199388