#pragma GCC target ("avx")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define _USE_MATH_DEFINES
#include<iostream>
#include<string>
#include<queue>
#include<cmath>
#include<map>
#include<set>
#include<list>
#include<iomanip>
#include<vector>
#include<random>
#include<functional>
#include<algorithm>
#include<stack>
#include<cstdio>
#include<cstring>
#include<bitset>
#include<unordered_map>
#include<climits>
#include<fstream>
#include<complex>
#include<time.h>
#include<cassert>
#include<functional>
#include<numeric>
#include<tuple>
using namespace std;
using ll = long long;
using ld = long double;
#define int long long
#define all(a) (a).begin(),(a).end()
#define fs first
#define sc second
#define xx first
#define yy second.first
#define zz second.second
#define C complex<ld>
#define H pair<int, int>
#define P pair<int, pair<int, int>>
#define Q(i,j,k) mkp(i,mkp(j,k))
#define rng(i,s,n) for(int i = (s) ; i < (n) ; i++)
#define rep(i,n) rng(i, 0, (n))
#define mkp make_pair
#define vec vector
#define vi vec<int>
#define pb emplace_back
#define siz(a) (a).size()
#define crdcomp(b) sort(all((b)));(b).erase(unique(all((b))),(b).end())
#define getidx(b,i) lower_bound(all(b),(i))-b.begin()
#define ssp(i,n) (i==(int)(n)-1?"\n":" ")
#define ctoi(c) (int)(c-'0')
#define itoc(c) (char)(c+'0')
#define cyes printf("Yes\n")
#define cno printf("No\n")
#define cdf(n) int quetimes_=(n);rep(qq123_,quetimes_)
#define gcj printf("Case #%lld: ",qq123_+1)
#define readv(a,n) a.resize(n,0);rep(i,(n)) a[i]=read()
//#define endl "\n"
constexpr int mod = 1e9 + 7;
constexpr int Mod = 998244353;
constexpr int MXN = 500000 + 100;
constexpr ld EPS = 1e-10;
constexpr ll inf = 3 * 1e18;
constexpr int Inf = 15 * 1e8;
const vec<int>dx{ -1,1,0,0 }, dy{ 0,0,-1,1 };
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
ll read() { ll u, k = scanf("%lld", &u); return u; }
string reads() { string s; cin >> s; return s; }
H readh(bool g = 0) { H u; int k = scanf("%lld %lld", &u.fs, &u.sc); if (g) u.fs--, u.sc--; return u; }
bool ina(H t, int h, int w) { return 0 <= t.fs && t.fs < h && 0 <= t.sc && t.sc < w; }
bool ina(int t, int l, int r) { return l <= t && t < r; }
ll gcd(ll i, ll j) { return j ? gcd(j, i % j) : i; }
ll popcount(ll x) {
	int sum = 0; for (int i = 0; i < 60; i++)if ((1ll << i) & x) sum++;
	return sum;
}
class mint {
public:int v;
	  mint(int v = 0) { s(v % mod); }
	  constexpr static int mod = 1e9 + 7;
	  constexpr static int fn_ = 500005;
	  static mint fact[fn_], comp[fn_];
	  mint pow(mint x) const {
		  mint b(v), c(1);
		  while (x.v) {
			  if (x.v & 1) c *= b;
			  b *= b;
			  x.v >>= 1;
		  }
		  return c;
	  }
	  inline mint& s(int vv) {
		  v = vv < mod ? vv : vv - mod;
		  return *this;
	  }
	  mint pow(int x) const { return pow(mint(x)); }
	  mint inv()const { return pow(mod - 2); }
	  mint operator-()const { return mint() - *this; }
	  mint& operator+=(const mint b) { return s(v + b.v); }
	  mint& operator-=(const mint b) { return s(v + mod - b.v); }
	  mint& operator*=(const mint b) { v = v * b.v % mod; return *this; }
	  mint& operator/=(const mint b) { (*this) *= b.inv(); }
	  mint operator+(const mint b) const { return mint(v) += b; }
	  mint operator-(const mint b) const { return mint(v) -= b; }
	  mint operator*(const mint b) const { return mint(v) *= b; }
	  mint operator/(const mint b) const { return mint(v) /= b; }
	  mint& operator+=(const int b) { v = (v + b) % mod; return *this; }
	  mint& operator-=(const int b) { v = (v - b) % mod + mod; return s(v); }
	  mint& operator*=(const int b) { v = v * b % mod; return *this; }
	  mint& operator/=(const int b) { (*this) *= mint(b).inv(); }
	  mint operator+(const int b) const { return mint(v) += b; }
	  mint operator-(const int b) const { return mint(v) -= b; }
	  mint operator*(const int b) const { return mint(v) *= b; }
	  mint operator/(const int b) const { return mint(v) /= b; }
	  friend ostream& operator<<(ostream& os, const mint& m) {
		  return os << m.v;
	  }
	  friend istream& operator>>(istream& is, mint& m) {
		  int x; is >> x; m = mint(x);
		  return is;
	  }
	  bool operator<(const mint& r)const { return v < r.v; }
	  bool operator>(const mint& r)const { return v > r.v; }
	  bool operator==(const mint& r)const { return v == r.v; }
	  bool operator!=(const mint& r)const { return v != r.v; }
	  explicit operator bool()const { return v; }
	  mint comb(mint k) {
		  if (k > * this) return mint();
		  if (!fact[0]) combini();
		  if (v >= fn_) {
			  if (k > * this - k) k = *this - k;
			  mint tmp(1);
			  for (int i = v; i >= v - k.v + 1; i--) tmp *= mint(i);
			  return comp[k.v];
		  }
		  else return fact[v] * comp[k.v] * comp[v - k.v];
	  }//nCk
	  mint comb(int k) { return comb(mint(k)); }
	  static void combini() {
		  fact[0] = 1;
		  for (int i = 1; i < fn_; i++) fact[i] = fact[i - 1] * mint(i);
		  comp[fn_ - 1] = fact[fn_ - 1].inv();
		  for (int i = fn_ - 2; i >= 0; i--) comp[i] = comp[i + 1] * mint(i + 1);
	  }
}; mint mint::fact[fn_], mint::comp[fn_];
//--------------------------------------------------------------
class UnionFind {
public:
	int size = 0;
	int pa[500000];
	void init(int n) {
		size = n;
		for (int i = 0; i <= size; i++) pa[i] = -1;
	}
	int find(int x) {
		if (pa[x] < 0) return x;
		return pa[x] = find(pa[x]);
	}
	bool unite(int x, int y) {
		x = find(x); y = find(y);
		if (x == y) return false;
		if (pa[x] > pa[y]) swap(x, y);
		pa[x] += pa[y];
		pa[y] = x;
		return true;
	}
	bool same(int x, int y) {
		return find(x) == find(y);
	}
	bool isroot(int x) {
		return x == find(x);
	}
	int sz(int x) {
		return -pa[find(x)];
	}
	H operator[](int x) {
		x = find(x);
		return H{ x,-pa[x] };
	}
};
UnionFind uf;
signed main() {
	int n = read();
	vec<int> p; readv(p, n);
	rep(i, n) if (p[i] > 0) p[i]--;
	uf.init(n);
	rep(i, n)if (p[i] != -1) uf.unite(i, p[i]);

	vec<int>es(n);
	rep(i, n)if (p[i] != -1)es[uf[i].fs]++;

	int f = count(all(p), -1);
	mint ans;
	rep(i, n)if (uf.isroot(i) && es[i] == uf.sz(i)) {
		ans += mint(n - 1).pow(f);
	}
	//前処理で足しておく

	vec<int>x;
	rep(i, n)if (uf.isroot(i) && es[i] != uf.sz(i)) x.pb(uf.sz(i));
	int s = siz(x);
	//木の集合のサイズを全列挙、木の集合の数

	vec<mint>dp(s + 1);
	dp[0] = 1;

	for (auto v : x) {
		for (int i = s - 1; i >= 0; i--) {
			dp[i + 1] += dp[i] * v;
		}
	}

	mint::combini();
	rng(i, 2, s + 1)
		ans += mint(n - 1).pow(s - i) * dp[i] * mint::fact[i - 1];

	for (auto v : x) {
		ans += mint(n - 1).pow(s - 1) * (v - 1);
	}
	ans = mint(n - 1).pow(f) * n - ans;
	//全ての場合の辺の数-すべての場合の閉路の数
	cout << ans << endl;
}

Measured memory_bytes: 11736