#include <bits/stdc++.h>

using namespace std;

const int MOD = 1000000007; // 998244353; // 998244853; 

template <typename T>
struct modular {
    constexpr modular() : val(0){}
    constexpr modular(const modular<T>& _m) : val(_m.val) {}
    template <typename U> constexpr modular(const U& _r = U()) {
        val = -MOD <= _r && _r < MOD ? _r: _r % MOD;
        if (val < 0) { val += MOD; } }
    const T operator()() { return val; }
    template <typename U> explicit operator U() const { return static_cast<U>(val); }
    modular<T>& operator+=(const modular<T>& _m) { if ((val += _m.val) >= MOD) { val -= MOD; } return *this; }
    modular<T>& operator-=(const modular<T>& _m) { if ((val -= _m.val) < 0) { val += MOD; } return *this; }
    modular<T>& operator*=(const modular<T>& _m) { val = modular<T>(static_cast<int64_t>(val) * static_cast<int64_t>(_m.val)).val; return *this; }
    modular<T>& operator/=(const modular<T>& _m) {
        T a = _m.val, b = MOD, u = 0, v = 1;
        while (a != 0) {
            T q = b / a;
            b -= q * a; swap(a, b);
            u -= q * v; swap(u, v); 
        } return *this *= u; }
    modular<T>& operator =(const modular<T>& _m) { val = _m.val; return *this; }
    template <typename U> modular<T>& operator+=(const U& _r) { return *this += modular<T>(_r); }
    template <typename U> modular<T>& operator-=(const U& _r) { return *this -= modular<T>(_r); }
    template <typename U> modular<T>& operator*=(const U& _r) { return *this *= modular<T>(_r); }
    template <typename U> modular<T>& operator/=(const U& _r) { return *this /= modular<T>(_r); } 
    template <typename U> modular<T>& operator =(const U& _r) { val = modular<T>(_r).val; return *this; }
    modular<T> operator-() { return modular<T>(-val); }    
    template <typename U> friend bool operator==(const modular<U>&, const modular<U>&);
    friend std::istream& operator>>(std::istream& os, modular<T>& _m) { os >> _m.val; _m *= 1; return os; }
    friend std::ostream& operator<<(std::ostream& os, const modular<T>& _m) { return os << _m.val; }
    template <typename U>
    modular<T> exp(U e) {
        modular<T> res = 1;
        modular<T> b = val;
        if (e < 0) { b = 1/b; e *= -1; }
        for (; e; e >>= 1) {
            if (e & 1) { res *= b; }
            b *= b;
        } return res; }
private:
    T val;
};
template <typename T> inline modular<T> operator+(const modular<T>& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) += _rhs; }
template <typename T, typename U> inline modular<T> operator+(const modular<T>& _lhs, const U& _rhs) { return modular<T>(_lhs) += _rhs; }
template <typename T, typename U> inline modular<T> operator+(const U& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) += _rhs; }
template <typename T> inline modular<T> operator-(const modular<T>& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) -= _rhs; }
template <typename T, typename U> inline modular<T> operator-(const modular<T>& _lhs, const U& _rhs) { return modular<T>(_lhs) -= _rhs; }
template <typename T, typename U> inline modular<T> operator-(const U& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) -= _rhs; }
template <typename T> inline modular<T> operator*(const modular<T>& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) *= _rhs; }
template <typename T, typename U> inline modular<T> operator*(const modular<T>& _lhs, const U& _rhs) { return modular<T>(_lhs) *= _rhs; }
template <typename T, typename U> inline modular<T> operator*(const U& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) *= _rhs; }
template <typename T> inline modular<T> operator/(const modular<T>& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) /= _rhs; }
template <typename T, typename U> inline modular<T> operator/(const modular<T>& _lhs, const U& _rhs) { return modular<T>(_lhs) /= _rhs; }
template <typename T, typename U> inline modular<T> operator/(const U& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) /= _rhs; }
template <typename T> inline bool operator==(const modular<T>& _lhs, const modular<T>& _rhs) { return _lhs.val == _rhs.val; }
template <typename T, typename U> inline bool operator==(const modular<T>& _lhs, const U& _rhs) { return _lhs == modular<T>(_rhs); }
template <typename T, typename U> inline bool operator==(const U& _lhs, const modular<T>& _rhs) { return modular<T>(_lhs) == _rhs; }
template <typename T> inline bool operator!=(const modular<T>& _lhs, const modular<T>& _rhs) { return !(_lhs == _rhs); }
template <typename T, typename U> inline bool operator!=(const modular<T>& _lhs, const U& _rhs) { return !(_lhs == _rhs); }
template <typename T, typename U> inline bool operator!=(const U& _lhs, const modular<T>& _rhs) { return !(_lhs == _rhs); }
typedef modular<int> mint;

struct Dsu {
    int n;
    vector<int> p;
    vector<int> r;
    
    Dsu(int _n) : n(_n)
        , p(n)
        , r(n)
    {
        init();
    }
    inline void init() {
        for (int i = 0; i < n; i++) {
            p[i] = i;
            r[i] = 1;
        }
    }
    inline int find(int x) {
        return p[x] == x ? x: p[x] = find(p[x]);
    }
    inline bool join(int x, int y) {
        x = find(x); y = find(y);
        if (x == y) return false;
        if (r[x] < r[y]) swap(x, y);
        p[y] = x; r[x] += r[y];
        return true;
    }
    inline bool check(int x, int y) {
        return find(x) == find(y);
    }
    inline int size(int x) {
        return r[find(x)];
    }
};

void solve() {
    int n; cin >> n;
    Dsu d(n);
    int got = 0;
    vector<bool> del(n);
    for (int i = 0; i < n; i++) {
        int x; cin >> x; --x;
        if (x >= 0) {
            //if (!d.join(i, x)) {
            //    ++got;
            //    del[d.find(i)] = true;
            //}
            if (d.check(i, x)) {
                ++got;
                del[i] = true;
            } else {
                d.join(i, x);
            }
        }
    }
    for (int i = 0; i < n; i++) {
        if (del[i]) del[d.find(i)] = true;
    }
    vector<int> a;
    for (int i = 0; i < n; i++) {
        if (!del[i] && i == d.find(i)) {
            a.push_back(d.size(i));
        }
    }

    int m = a.size();
    mint res = got * mint(n-1).exp(m);
    vector<mint> dp(m + 1);
    dp[0] = 1;
    for (int x: a) {
        for (int i = m-1; i >= 0; i--) {
            dp[i+1] += dp[i] * x;
        }
    }
    for (int x: a) res += (x-1) * mint(n-1).exp(m-1);
    mint fac = 1;
    for (int i = 2; i <= m; i++) {
        res += dp[i] *fac* mint(n-1).exp(m-i);
        fac *= i;
    }

    res = n*mint(n-1).exp(m) - res;
    cout << res;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    solve();
    return 0;
}


Measured memory_bytes: 3676