#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
#include<complex>
#include<numeric>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
constexpr ll mod = 1000000007;
const ll INF = mod * mod;
typedef pair<int, int>P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;
typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-12;
const ld pi = acos(-1.0);

void chmin(ll &a, ll b) {
	a = min(a, b);
}
void chmax(ll &a, ll b) {
	a = max(a, b);
}
ll mod_pow(ll a, ll n, ll m = mod) {
	a %= m;
	ll res = 1;
	while (n) {
		if (n & 1)res = res * a%m;
		a = a * a%m; n >>= 1;
	}
	return res;
}

struct modint {
	ll n;
	modint() :n(0) { ; }
	modint(ll m) :n(m) {
		if (n >= mod)n %= mod;
		else if (n < 0)n = (n%mod + mod) % mod;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint &a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; }
modint operator-=(modint &a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; }
modint operator*=(modint &a, modint b) { a.n = ((ll)a.n*b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, int n) {
	if (n == 0)return modint(1);
	modint res = (a*a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p%a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }
const int max_n = 1 << 18;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}

int dx[4] = { 0,1,0,-1 };
int dy[4] = { 1,0,-1,0 };

struct uf {
private:
	vector<int> par, ran;
public:
	uf(int n) {
		par.resize(n, 0);
		ran.resize(n, 0);
		rep(i, n) {
			par[i] = i;
		}
	}
	int find(int x) {
		if (par[x] == x)return x;
		else return par[x] = find(par[x]);
	}
	void unite(int x, int y) {
		x = find(x), y = find(y);
		if (x == y)return;
		if (ran[x] < ran[y]) {
			par[x] = y;
		}
		else {
			par[y] = x;
			if (ran[x] == ran[y])ran[x]++;
		}
	}
	bool same(int x, int y) {
		return find(x) == find(y);
	}
};

modint dp[5001][5001];
void solve() {
	int n; cin >> n;
	vector<int> p(n);
	rep(i, n) {
		cin >> p[i]; p[i]--;
	}
	uf u(n);
	rep(i, n)if (p[i] >= 0) {
		u.unite(i, p[i]);
	}
	vector<int> trans(n);
	vector<bool> used(n, false);
	int tmp = 0;
	rep(i, n) {
		int par = u.find(i);
		if (used[par])continue;
		used[par] = true;
		trans[par] = tmp;
		tmp++;
	}
	vector<int> cnt(tmp);
	vector<bool> exi(tmp);
	rep(i, n) {
		int par = u.find(i);
		par = trans[par];
		cnt[par]++;
		if (p[i] < 0) {
			exi[par] = true;
		}
	}

	vector<int> als;
	rep(i, tmp)if (exi[i]) {
		als.push_back(cnt[i]);
	}
	int sz = als.size();
	dp[0][0] = 1;
	rep(i, sz) {
		rep(j, i + 1) {
			dp[i + 1][j + 1] += dp[i][j] * (modint)als[i];
			dp[i + 1][j] += (modint)(n-1)*dp[i][j];
		}
	}
	//cout << dp[sz][2] << "\n";
	modint ans = (modint)(n)*(modint)mod_pow(n-1,sz);


	Rep1(x,2, sz) {
		ans -=fact[x-1]*dp[sz][x];
	}
	rep(i, sz) {
		ans -= (modint)(als[i] - 1)*(modint)mod_pow(n - 1, sz-1);
	}
	//cout << "? " << ans << "\n";
	modint memo = ans;
	rep(i, tmp)if(!exi[i]) {
		ans -= (modint)mod_pow(n - 1, sz);
	}
	//cout << ans - memo << "\n";
	cout << ans << "\n";
}


signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	init_f();
	//init();
	//int t; cin >> t; rep(i, t)solve();
	solve();
	stop
		return 0;
}


Measured memory_bytes: 203312