#line 1 "temp0.cpp"
//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <utility>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

struct rep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
struct revrep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) noexcept {
  return a < b ? b - a : a - b;
}
template <class T> void chmin(T &a, const T &b) noexcept {
  if (b < a)
    a = b;
}
template <class T> void chmax(T &a, const T &b) noexcept {
  if (a < b)
    a = b;
}
template <class F> class rec_lambda {
  F f;

public:
  rec_lambda(F &&f) : f(std::move(f)) {}
  template <class... Args> auto operator()(Args &&... args) const {
    return f(*this, std::forward<Args>(args)...);
  }
};
template <class F> auto make_rec(F &&f) { return rec_lambda<F>(std::move(f)); }
template <class T> T scan() {
  T ret;
  std::cin >> ret;
  return ret;
}

} // namespace n91

#line 1 "/mnt/c/Users/noshi/Desktop/base_/Library/other/modint.cpp"
#include <cstdint>

template <std::uint_fast64_t Modulus> class modint {
  using u64 = std::uint_fast64_t;

public:
  using value_type = u64;

  static constexpr u64 mod = Modulus;

private:
  static_assert(mod < static_cast<u64>(1) << 32,
                "Modulus must be less than 2**32");

  u64 v;

  constexpr modint &negate() noexcept {
    if (v != 0)
      v = mod - v;
    return *this;
  }

public:
  constexpr modint(const u64 x = 0) noexcept : v(x % mod) {}
  constexpr u64 &value() noexcept { return v; }
  constexpr const u64 &value() const noexcept { return v; }
  constexpr modint operator+() const noexcept { return modint(*this); }
  constexpr modint operator-() const noexcept { return modint(*this).negate(); }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    v += rhs.v;
    if (v >= mod)
      v -= mod;
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (v < rhs.v)
      v += mod;
    v -= rhs.v;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    v = v * rhs.v % mod;
    return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
    u64 exp = mod - 2;
    while (exp != 0) {
      if (exp % 2 != 0)
        *this *= rhs;
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }
};
template <std::uint_fast64_t Modulus>
constexpr typename modint<Modulus>::u64 modint<Modulus>::mod;
#line 84 "temp0.cpp"

namespace n91 {

void main_() {
  /*
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  //*/
  using mint = modint<1000000007>;

  const usize n = scan<usize>();

  usize ln = 0, gn = 0;

  std::vector<mint> le(n, 0), ge(n, 0);
  for (const usize i : rep(0, n)) {
    switch (scan<int>()) {
    case 1: {
      gn += 1;
      const usize x = scan<usize>() - 1;
      for (const usize j : rep(x, n))
        ge[j] += 1;
    } break;
    case 0: {
      ln += 1;
      const usize x = scan<usize>() - 1;
      for (const usize j : rep(0, x + 1))
        le[j] += 1;
    } break;
    }
  }

  auto dp = md_vec(ln + 1, gn + 1, mint(0));
  dp[0][0] = 1;
  for (const usize i : rep(0, ln + 1)) {
    for (const usize j : rep(0, gn + 1)) {
      if (i != ln && le[i + j].value() > (ln - i - 1)) {
        dp[i + 1][j] += dp[i][j] * (le[i + j] - (ln - i - 1));
      }
      if (j != gn && ge[i + j].value() > j) {
        dp[i][j + 1] += dp[i][j] * (ge[i + j] - j);
      }
    }
  }
  std::cout << dp[ln][gn].value() << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}