#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;
#define FI first
#define SE second
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))

constexpr lint MOD = 1000000007;

int main()
{
    int N;
    cin >> N;
    vector<int> A(N * 2);
    cin >> A;

    set<int> half, full, notused;
    REP(i, N)
    {
        if (A[i * 2] * A[i * 2 + 1] < 0) half.insert(-A[i * 2] * A[i * 2 + 1]);
        if (A[i * 2] > 0 and A[i * 2 + 1] > 0) full.insert(A[i * 2]), full.insert(A[i * 2 + 1]);
    }
    FOR(i, 1, 2 * N + 1) if (!half.count(i) and !full.count(i)) notused.insert(i);

    int L = N - full.size() / 2 - half.size(); // No. of empty pairs

    vector<vector<vector<lint>>> dp;
    ndarray(dp, 2, N * 2 + 1, N * 2 + 1);
    dp[0][0][0] = 1;

    int G = 0, H = 0;

    REP(i, 2 * N)
    {
        int n = 2 * N - i;
        REP(j, 2 * N + 1) REP(k, 2 * N + 1) dp[(i + 1) % 2][j][k] = 0;
        REP(j, 2 * N + 1) REP(k, 2 * N + 1) if (dp[i % 2][j][k])
        {
            int pa2 = G - j - k - (H - k) * 2;
            if (half.count(n))
            {
                // 既に見えている
                if (k < N * 2) (dp[(i + 1) % 2][j][k + 1] += dp[i % 2][j][k]) %= MOD;
                if (j > 0) (dp[(i + 1) % 2][j - 1][k] += dp[i % 2][j][k]) %= MOD;
            }
            else if (full.count(n))
            {
                // 既にペアまで決まっている（のでなにもしない）
                dp[(i + 1) % 2][j][k] = dp[i % 2][j][k];
            }
            else
            {
                // 見えていない
                if (j < N * 2) (dp[(i + 1) % 2][j + 1][k] += dp[i % 2][j][k]) %= MOD;
                if (j > 0) (dp[(i + 1) % 2][j - 1][k] += dp[i % 2][j][k] * (L - pa2 / 2)) %= MOD;
                if (k > 0) (dp[(i + 1) % 2][j][k - 1] += dp[i % 2][j][k] * k) %= MOD;
            }
        }
        G += !full.count(n);
        H += half.count(n);
    }
    cout << dp[0][0][0] << endl;
}


Measured memory_bytes: 6016