#ifndef CLASS_MODINT
#define CLASS_MODINT

#include <cstdint>

template <std::uint32_t mod>
class modint {
private:
	std::uint32_t n;
public:
	modint() : n(0) {};
	modint(std::int64_t n_) : n((n_ >= 0 ? n_ : mod - (-n_) % mod) % mod) {};
	static constexpr std::uint32_t get_mod() { return mod; }
	std::uint32_t get() const { return n; }
	bool operator==(const modint& m) const { return n == m.n; }
	bool operator!=(const modint& m) const { return n != m.n; }
	modint& operator+=(const modint& m) { n += m.n; n = (n < mod ? n : n - mod); return *this; }
	modint& operator-=(const modint& m) { n += mod - m.n; n = (n < mod ? n : n - mod); return *this; }
	modint& operator*=(const modint& m) { n = std::uint64_t(n) * m.n % mod; return *this; }
	modint operator+(const modint& m) const { return modint(*this) += m; }
	modint operator-(const modint& m) const { return modint(*this) -= m; }
	modint operator*(const modint& m) const { return modint(*this) *= m; }
	modint inv() const { return (*this).pow(mod - 2); }
	modint pow(std::uint64_t b) const {
		modint ans = 1, m = modint(*this);
		while (b) {
			if (b & 1) ans *= m;
			m *= m;
			b >>= 1;
		}
		return ans;
	}
};

#endif // CLASS_MODINT

#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
using mint = modint<1000000007>;
int main() {
	int N;
	cin >> N;
	vector<int> sa, sb;
	for (int i = 0; i < N; ++i) {
		int tp, x;
		cin >> tp >> x;
		if (tp == 0) sa.push_back(x);
		else sb.push_back(x - 1);
	}
	sort(sa.begin(), sa.end());
	sort(sb.begin(), sb.end());
	vector<vector<int> > ga(N + 1), gb(N + 1);
	for (int i = 0; i < sa.size(); ++i) {
		ga[sa[i]].push_back(i);
	}
	for (int i = 0; i < sb.size(); ++i) {
		gb[sb[i]].push_back(sb.size() - i - 1);
	}
	vector<vector<mint> > dp(sa.size() + 1, vector<mint>(sb.size() + 1));
	for (int i = 0; i <= sa.size(); ++i) {
		for (int j = 0; j <= sb.size(); ++j) {
			if (i == 0 && j == 0) {
				dp[i][j] = 1;
			}
			if (i >= 1) {
				dp[i][j] += dp[i - 1][j];
			}
			if (j >= 1) {
				dp[i][j] += dp[i][j - 1];
			}
			for (int k : ga[i + j]) {
				dp[i][j] *= max(i - k, 0);
			}
			for (int k : gb[i + j]) {
				dp[i][j] *= max(int(sb.size()) - j - k, 0);
			}
		}
	}
	cout << dp[sa.size()][sb.size()].get() << endl;
	return 0;
}