#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; typedef long long ll; typedef unsigned int ui; const ll mod = 1000000007; const ll INF = (ll)1000000007 * 1000000007; typedef pair P; #define stop char nyaa;cin>>nyaa; #define rep(i,n) for(int i=0;i=0;i--) #define Rep(i,sta,n) for(int i=sta;i=sta;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++) typedef long double ld; const ld eps = 1e-8; const ld pi = acos(-1.0); typedef pair LP; template struct ModInt { long long x; ModInt() : x(0) {} ModInt(long long y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} explicit operator int() const {return x;} 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; a -= t * b; swap(a, b); u -= t * v; swap(u, v); } return ModInt(u); } ModInt power(long long p) const{ int a = x; if (p==0) return 1; if (p==1) return ModInt(a); if (p%2==1) return (ModInt(a)*ModInt(a)).power(p/2)*ModInt(a); else return (ModInt(a)*ModInt(a)).power(p/2); } ModInt power(const ModInt p) const{ return ((ModInt)x).power(p.x); } friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; } friend istream &operator>>(istream &is, ModInt &a) { long long x; is >> x; a = ModInt(x); return (is); } }; using modint = ModInt; int n; vector x[2]; modint dp[3010][3010]; void solve(){ cin >> n; rep(i,n){ int t,s; cin >> t >> s; x[t].push_back(s-1); } sort(x[0].begin(),x[0].end()); sort(x[1].begin(),x[1].end()); int l=x[0].size(),m=x[1].size(); //cout << l << " " << m << endl; dp[0][0]=1; rep(i,l+1){ rep(j,m+1){ //cout << i << " " << j << " " << dp[i][j] << endl; if(i+1<=l){ int s=(x[0].end()-lower_bound(x[0].begin(),x[0].end(),i+j))-(l-i-1); //cout << s << endl; dp[i+1][j]+=(modint)max(s,0)*dp[i][j]; } if(j+1<=m){ int s=(upper_bound(x[1].begin(),x[1].end(),i+j)-x[1].begin())-j; //cout << s << endl; dp[i][j+1]+=(modint)max(s,0)*dp[i][j]; } } } cout << dp[l][m] << endl; } int main(){ ios::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(50); solve(); }