import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }

struct ModInt(int M_) {
  import std.conv : to;
  alias M = M_;
  int x;
  this(ModInt a) { x = a.x; }
  this(long a) { x = cast(int)(a % M); if (x < 0) x += M; }
  ref ModInt opAssign(long a) { return (this = ModInt(a)); }
  ref ModInt opOpAssign(string op)(ModInt a) {
    static if (op == "+") { x += a.x; if (x >= M) x -= M; }
    else static if (op == "-") { x -= a.x; if (x < 0) x += M; }
    else static if (op == "*") { x = cast(int)((cast(long)(x) * a.x) % M); }
    else static if (op == "/") { this *= a.inv(); }
    else static assert(false);
    return this;
  }
  ref ModInt opOpAssign(string op)(long a) {
    static if (op == "^^") {
      if (a < 0) return (this = inv()^^(-a));
      ModInt t2 = this, te = ModInt(1);
      for (long e = a; e > 0; e >>= 1) {
        if (e & 1) te *= t2;
        t2 *= t2;
      }
      x = cast(int)(te.x);
      return this;
    } else return mixin("this " ~ op ~ "= ModInt(a)");
  }
  ModInt inv() const {
    int a = x, b = M, y = 1, z = 0, t;
    for (; ; ) {
      t = a / b; a -= t * b;
      if (a == 0) {
        assert(b == 1 || b == -1);
        return ModInt(b * z);
      }
      y -= t * z;
      t = b / a; b -= t * a;
      if (b == 0) {
        assert(a == 1 || a == -1);
        return ModInt(a * y);
      }
      z -= t * y;
    }
  }
  ModInt opUnary(string op: "-")() const { return ModInt(-x); }
  ModInt opBinary(string op, T)(T a) const {
    return mixin("ModInt(this) " ~ op ~ "= a");
  }
  ModInt opBinaryRight(string op)(long a) const {
    return mixin("ModInt(a) " ~ op ~ "= this");
  }
  bool opCast(T: bool)() const { return (x != 0); }
  string toString() const { return x.to!string; }
}

enum MO = 10^^9 + 7;
alias Mint = ModInt!MO;


int root(int[] uf, int u) {
  return (uf[u] < 0) ? u : (uf[u] = uf.root(uf[u]));
}
bool connect(int[] uf, int u, int v) {
  u = uf.root(u);
  v = uf.root(v);
  if (u == v) return false;
  if (uf[u] > uf[v]) swap(u, v);
  uf[u] += uf[v];
  uf[v] = u;
  return true;
}


void main() {
  try {
    for (; ; ) {
      const N = readInt();
      auto P = new int[N];
      foreach (u; 0 .. N) {
        P[u] = readInt() - 1;
      }
      
      auto uf = new int[N];
      uf[] = -1;
      foreach (u; 0 .. N) {
        if (P[u] != -2) {
          uf.connect(u, P[u]);
        }
      }
      auto indeg = new int[N];
      foreach (u; 0 .. N) {
        if (P[u] != -2) {
          ++indeg[P[u]];
        }
      }
      auto numLeaves = new int[N];
      auto numRoots = new int[N];
      foreach (u; 0 .. N) {
        const r = uf.root(u);
        if (indeg[u] == 0) {
          ++numLeaves[r];
        }
        if (P[u] == -2) {
          ++numRoots[r];
        }
      }
      
      const total = Mint(N - 1)^^P.count(-2);
      
      Mint ans;
      
      int num;
      auto crt = [Mint(1)];
      foreach (r; 0 .. N) {
        if (uf[r] < 0) {
          debug {
            writeln(r, ": ", numLeaves[r], " ", numRoots[r]);
          }
          switch (numRoots[r]) {
            case 0: {
              ans += total;
            } break;
            case 1: {
              auto nxt = new Mint[num + 2];
              foreach (x; 0 .. num + 1) {
                nxt[x] += crt[x] * (N - 1);
                nxt[x + 1] += crt[x] * (-uf[r]);
              }
              crt = nxt;
              ++num;
            } break;
            default: assert(false);
          }
        }
      }
      debug {
        writeln("crt = ", crt);
      }
      
      Mint fac = 1;
      foreach (x; 1 .. num + 1) {
        ans += fac * crt[x];
        fac *= x;
      }
      
      foreach (u; 0 .. N) {
        if (P[u] == -2) {
          debug {
            writeln("- ", total / (N - 1));
          }
          ans -= total / (N - 1);
        }
      }
      
      ans = total * N - ans;
      writeln(ans);
      
      debug {
        int[] us;
        foreach (u; 0 .. N) {
          if (P[u] == -2) {
            us ~= u;
          }
        }
        const usLen = cast(int)(us.length);
        long brt;
        foreach (p; 0 .. N^^usLen) {
          auto ps = P.dup;
          foreach (j; 0 .. usLen) {
            ps[us[j]] = (p / N^^j) % N;
          }
          bool ok = true;
          foreach (u; 0 .. N) {
            ok = ok && (ps[u] != u);
          }
          if (ok) {
            auto ufBrt = new int[N];
            ufBrt[] = -1;
            foreach (u; 0 .. N) {
              ufBrt.connect(u, ps[u]);
            }
            const numComps = cast(int)(ufBrt.count!"a < 0");
            brt += N - numComps;
          }
        }
        writeln("brt = ", brt);
      }
    }
  } catch (EOFException e) {
  }
}


Measured memory_bytes: 7476