#include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vd = vector<double>;
using vs = vector<string>;

typedef tree<
ll,
null_type,
less<ll>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
// ordered_set X;
// *X.find_by_order(i) = ith largest element (counting from zero)
// X.order_of_key(k) = number of items in X < k (strict lt)

template<int MOD> struct modnum {
    int v;
    modnum() : v(0) {}
    modnum(ll _v) : v(_v % MOD) { if (v < 0) v += MOD; }
    explicit operator int() const { return v; }
    friend istream& operator >> (istream& i, modnum& n) { ll v; i >> v; n = modnum(v); return i; }
    friend ostream& operator << (ostream& o, const modnum& n) { return o << n.v; }

    friend bool operator == (const modnum& a, const modnum& b) { return a.v == b.v; }
    friend bool operator != (const modnum& a, const modnum& b) { return a.v != b.v; }

    modnum& operator += (const modnum& o) { v += o.v; if (v >= MOD) v -= MOD; return *this; }
    modnum& operator -= (const modnum& o) { v -= o.v; if (v < 0) v += MOD; return *this; }
    modnum& operator *= (const modnum& o) { v = int(ll(v) * ll(o.v) % MOD); return *this; }
    modnum operator - () { modnum res; if (v) res.v = MOD - v; return res; }
    friend modnum operator + (const modnum& a, const modnum& b) { return modnum(a) += b; }
    friend modnum operator - (const modnum& a, const modnum& b) { return modnum(a) -= b; }
    friend modnum operator * (const modnum& a, const modnum& b) { return modnum(a) *= b; }

    modnum pow(ll e) const {
        if (e == 0) return 1;
        if (e & 1) return *this * this->pow(e-1);
        return (*this * *this).pow(e/2);
    }

    modnum inv() const {
        int g = MOD, x = 0, y = 1;
        for (int r = v; r != 0; ) {
            int q = g / r;
            g %= r; swap(g, r);
            x -= q * y; swap(x, y);
        }

        assert(g == 1);
        assert(y == MOD || y == -MOD);
        return x < 0 ? x + MOD : x;
    }
    modnum& operator /= (const modnum& o) { return (*this) *= o.inv(); }
    friend modnum operator / (const modnum& a, const modnum& b) { return modnum(a) /= modnum(b); }

    static int totient() {
        int tot = MOD, tmp = MOD;
        for (int p = 2; p * p <= tmp; p++) if (tmp % p == 0) {
            tot = tot / p * (p - 1);
            while (tmp % p == 0) tmp /= p;
        }
        if (tmp > 1) tot = tot / tmp * (tmp - 1);
        return tot;
    }

    static int primitive_root() {
        if (MOD == 1) return 0;
        if (MOD == 2) return 1;

        int tot = totient(), tmp = tot;
        vi tot_pr;
        for (int p = 2; p * p <= tmp; p++) if (tot % p == 0) {
            tot_pr.push_back(p);
            while (tmp % p == 0) tmp /= p;
        }
        if (tmp > 1) tot_pr.push_back(tmp);

        for (int r = 2; r < MOD; r++) if (__gcd(r, MOD) == 1) {
            bool root = true;
            for (int p : tot_pr) root &= modnum(r).pow(tot / p) != 1;
            if (root) return r;
        }
        assert(false);
    }

    static modnum generator() { static modnum g = primitive_root(); return g; }
    static int discrete_log(modnum v) {
        static const int M = ceil(sqrt(MOD));
        static unordered_map<int, int> table;
        if (table.empty()) {
            modnum e = 1;
            for (int i = 0; i < M; i++) { table[e.v] = i; e *= generator(); }
        }
        static modnum f = generator().pow(totient() - M);

        for (int i = 0; i < M; i++) {
            if (table.count(v.v)) return table[v.v] + i * M;
            v *= f;
        }
        assert(false);
    }

    static modnum fact(int n) {
        static vector<modnum<MOD>> fact = { 1 };
        for (assert(n >= 0); fact.size() <= n; )
            fact.push_back(fact.back() * fact.size());
        return fact[n];
    }

    static modnum finv(int n) {
        static vector<modnum<MOD>> finv = { 1 };
        for (assert(n >= 0); finv.size() <= n; )
            finv.push_back(finv.back() / finv.size());
        return finv[n];
    }

    static modnum ncr(int n, int r) {
        if (r < 0 || n < r) return 0;
        return fact(n) * finv(r) * finv(n - r);
    }
};

constexpr ll MOD = 1e9 + 7;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int N;
    cin >> N;

    vi P(N);
    for (int i=0;i<N;i++) {
        cin >> P[i];
        if(P[i] > 0) P[i]--;
    }

    vvi adj(N);
    for (int i=0;i<N;i++) {
        if (P[i]!=-1) {
            adj[i].push_back(P[i]);
            adj[P[i]].push_back(i);
        }
    }

    vi comps(N, -1);
    vi scomps;
    int ncomps = 0;
    for (int i=0;i<N;i++) {
        if (comps[i] == -1) {
            queue<int> bfs;
            bfs.push(i);
            comps[i] = ncomps;
            int cursz = 0;

            while (!bfs.empty()) {
                int cur = bfs.front();
                bfs.pop();
                cursz++;

                for (int nbr : adj[cur]) {
                    if (comps[nbr] == -1) {
                        comps[nbr] = ncomps;
                        bfs.push(nbr);
                    }
                }
            }

            scomps.push_back(cursz);

            ncomps++;
        }
    }

    int K = 0;
    for (int i=0;i<N;i++) if (P[i] == -1) K++;

    modnum<MOD> nm1 = N-1;
    modnum<MOD> ans = (N - ncomps) * nm1.pow(K);

    set<int> nzs;
    for (int i=0;i<N;i++) {
        if (P[i] == -1) {
            int csz = scomps[comps[i]];
            ans += (N - csz) * nm1.pow(K-1);
            nzs.insert(comps[i]);
        }
    }

    vi nzvs;
    for (int c : nzs) {
        nzvs.push_back(scomps[c]);
    }

    int M = nzvs.size();
    vector<modnum<MOD>> symsumrow(M+1, 0);
    vector<vector<modnum<MOD>>> symsums(M+1, symsumrow);
    // symsums[i][j] = j-cyclic sums of first i variables
    for (int i=0;i<=M;i++) symsums[i][0] = 1;
    for (int j=1;j<=M;j++) {
        for (int i=j;i<=M;i++) {
            symsums[i][j] = symsums[i-1][j] + nzvs[i-1]*symsums[i-1][j-1];
        }
    }
    // cout << nzvs.size() << endl;
    // for (auto x : nzvs) cout << x << " ";
    // cout << endl;
    // for (int i=0;i<=M;i++) cout << symsums[M][i] << " ";
    // cout << endl;

    

    modnum<MOD> excess = 0;
    for (int i=2;i<=M;i++) {
        excess += modnum<MOD>::fact(i-1) * symsums[M][i] * nm1.pow(K-i);
    }

    ans -= excess;
    cout << ans << endl;

    return 0;
}

Measured memory_bytes: 101640