#include // clang-format off #define pb push_back #define eb emplace_back #define fi first #define se second #define each(x,v) for(auto& x : v) #define all(v) (v).begin(),(v).end() #define sz(v) ((int)(v).size()) #define ini(...) int __VA_ARGS__; in(__VA_ARGS__) #define inl(...) long long __VA_ARGS__; in(__VA_ARGS__) #define ins(...) string __VA_ARGS__; in(__VA_ARGS__) #ifdef ONLINE_JUDGE #define rep(i,N) for(int i = 0; i < (int)(N); i++) #define repr(i,N) for(int i = (int)(N) - 1; i >= 0; i--) #define rep1(i,N) for(int i = 1; i <= (int)(N) ; i++) #define repr1(i,N) for(int i = (N) ; (int)(i) > 0 ; i--) #else #define rep(i,N) for(long long i = 0; i < (long long)(N); i++) #define repr(i,N) for(long long i = (long long)(N) - 1; i >= 0; i--) #define rep1(i,N) for(long long i = 1; i <= (long long)(N) ; i++) #define repr1(i,N) for(long long i = (N) ; (long long)(i) > 0 ; i--) #endif using namespace std; void solve(); using ll = long long; template using V = vector; using vi = V; using vl = V<>; using vvi = V< V >; constexpr int inf = 1001001001; constexpr ll infLL = (1LL << 61) - 1; struct IoSetupNya {IoSetupNya() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(7);} } iosetupnya; template inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; } template inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; } template ostream& operator <<(ostream& os, const pair &p) { os << p.first << " " << p.second; return os; } template istream& operator >>(istream& is, pair &p) { is >> p.first >> p.second; return is; } template ostream& operator <<(ostream& os, const vector &v) { int s = (int)v.size(); for(int i=0;i istream& operator >>(istream& is, vector &v) { for(auto &x : v) is >> x; return is; } void in(){} template void in(T &t,U &...u){ cin >> t; in(u...);} void out(){cout << "\n";} template void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);} templatevoid die(T x){out(x); exit(0);} #ifdef NyaanDebug #include "NyaanDebug.h" #define trc(...) do { cerr << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);} while(0) #define trca(v,N) do { cerr << #v << " = "; array_out(v , N);} while(0) #define trcc(v) do { cerr << "name : " << #v << "\n"; int cnt = 0; each(x , v){cerr << (cnt++) << " : "; trc(x); } } while(0) #else #define trc(...) #define trca(...) #define trcc(...) int main(){solve();} #endif #define inc(...) char __VA_ARGS__; in(__VA_ARGS__) #define in2(s,t) rep(i,sz(s)){in(s[i] , t[i]);} #define in3(s,t,u) rep(i,sz(s)){in(s[i] , t[i] , u[i]);} using vd = V; using vs = V; using vvl = V< V<> >; templatell ceil(T a,U b){return (a + b - 1) / b;} using P = pair; using vp = V

; constexpr int MOD = /**/ 1000000007; //*/ 998244353; // clang-format on /////////////////////////////////////////////////////////// template< int mod > struct ModInt { int x; ModInt() : x(0) {} ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} ModInt &operator+=(const ModInt &p) { if((x += p.x) >= mod) x -= mod; return *this; } ModInt &operator-=(const ModInt &p) { if((x += mod - p.x) >= mod) x -= mod; return *this; } ModInt &operator*=(const ModInt &p) { x = (int) (1LL * x * p.x % mod); return *this; } ModInt &operator/=(const ModInt &p) { *this *= p.inverse(); return *this; } ModInt operator-() const { return ModInt(-x); } ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; } ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; } ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; } ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; } bool operator==(const ModInt &p) const { return x == p.x; } bool operator!=(const ModInt &p) const { return x != p.x; } ModInt inverse() const { int a = x, b = mod, u = 1, v = 0, t; while(b > 0) { t = a / b; swap(a -= t * b, b); swap(u -= t * v, v); } return ModInt(u); } ModInt pow(int64_t n) const { ModInt ret(1), mul(x); while(n > 0) { if(n & 1) ret *= mul; mul *= mul; n >>= 1; } return ret; } friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; } friend istream &operator>>(istream &is, ModInt &a) { int64_t t; is >> t; a = ModInt< mod >(t); return (is); } static int get_mod() { return mod; } }; using modint = ModInt< MOD >; using vm = vector; modint dp[3030][3030][2]; vector fac,finv,inv; void cominit(int MAX) { MAX++; fac.resize(MAX , 0); finv.resize(MAX , 0); inv.resize(MAX , 0); fac[0] = fac[1] = finv[0] = finv[1] = inv[1] = 1; for (int i = 2; i < MAX; i++){ fac[i] = fac[i - 1] * i % MOD; inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD; finv[i] = finv[i - 1] * inv[i] % MOD; } } // nCk combination inline long long COM(int n,int k){ if(n < k || k < 0 || n < 0) return 0; else return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD; } // nPk permutation inline long long PER(int n,int k){ if (n < k || k < 0 || n < 0) return 0; else return (fac[n] * finv[n - k]) % MOD; } // nHk homogeneous polynomial inline long long HGP(int n,int k){ if(n == 0 && k == 0) return 1; // depending on problem? else if(n < 1 || k < 0) return 0; else return fac[n + k - 1] * (finv[k] * finv[n - 1] % MOD) % MOD; } void solve(){ ini(N); vi c(N),a(N); in2(c , a); auto mkord = [&](int n , auto f) -> vector{ vector ord(n); iota(begin(ord) , end(ord) , 0); sort(begin(ord) , end(ord) , f); return ord; }; vector ord = mkord(N , [&](int x,int y){ return (c[x]?a[x]-1:a[x]) < (c[y]?a[y]-1:a[y]); }); trc(ord); dp[0][0][0] = 1; // j個使った // 少なくともf個は条件を満たしていない(悲しいね) rep(i , N) rep(j , N) rep(f , 2){ modint cur = dp[i][j][f]; trc(i,j,f,cur); if(cur == 0) continue; int idx = ord[i]; if(c[idx] == 0){ dp[i + 1][j + 1][f] += cur * (a[idx] - j); } else{ dp[i + 1][j][f] += cur; dp[i + 1][j + 1][f ^ 1] += cur * (a[idx] - 1 - j); } } cominit(N * 5); modint ans = 0; rep(j , N + 1) rep(f , 2){ trc(dp[N][j][f]); if(f) ans += dp[N][j][f] * fac[N - j]; else ans -= dp[N][j][f] * fac[N - j]; } out(modint(0) - ans); }