#include <iostream>
#include <algorithm>
#include <utility>
#include <vector>
#include <numeric>
#include <tuple>

template <class T, class U>
inline bool chmin(T &lhs, const U &rhs) {
  if (lhs > rhs) {
    lhs = rhs;
    return true;
  }
  return false;
}

template <class T, class U>
inline bool chmax(T &lhs, const U &rhs) {
  if (lhs < rhs) {
    lhs = rhs;
    return true;
  }
  return false;
}

// [l, r) from l to r
struct range {
  struct itr {
    int i;
    constexpr itr(int i_): i(i_) { }
    constexpr void operator ++ () { ++i; }
    constexpr int operator * () const { return i; }
    constexpr bool operator != (itr x) const { return i != x.i; }
  };
  const itr l, r;
  constexpr range(int l_, int r_): l(l_), r(std::max(l_, r_)) { }
  constexpr itr begin() const { return l; }
  constexpr itr end() const { return r; }
};

// [l, r) from r to l
struct revrange {
  struct itr {
    int i;
    constexpr itr(int i_): i(i_) { }
    constexpr void operator ++ () { --i; }
    constexpr int operator * () const { return i; }
    constexpr bool operator != (itr x) const { return i != x.i; }
  };
  const itr r, l;
  constexpr revrange(int l_, int r_): l(l_ - 1), r(std::max(l_, r_) - 1) { }
  constexpr itr begin() const { return r; }
  constexpr itr end() const { return l; }
};

template <class T>
class modulo_int {
public:
  static constexpr int mod = T::value;
  static_assert(mod > 0, "mod must be positive");
private:
  long long value;
  constexpr void normalize() {
    value %= mod;
    if (value < 0) value += mod;
  }
public:
  constexpr modulo_int(long long value_ = 0): value(value_) { normalize(); }
  constexpr modulo_int operator - () const { return modulo_int(mod - value); }
  constexpr modulo_int operator ~ () const { return power(mod - 2); }
  constexpr long long operator () () const { return value; }
  constexpr modulo_int operator + (const modulo_int &rhs) const { return modulo_int(*this) += rhs; }
  constexpr modulo_int &operator += (const modulo_int &rhs) {
    if ((value += rhs.value) >= mod) value -= mod;
    return (*this);
  }
  constexpr modulo_int operator - (const modulo_int &rhs) const { return modulo_int(*this) -= rhs; }
  constexpr modulo_int &operator -= (const modulo_int &rhs) {
    if ((value += mod - rhs.value) >= mod) value -= mod;
    return (*this);
  }
  constexpr modulo_int operator * (const modulo_int &rhs) const { return modulo_int(*this) *= rhs; }
  constexpr modulo_int &operator *= (const modulo_int &rhs) {
    (value *= rhs.value) %= mod;
    return (*this);
  }
  constexpr modulo_int operator / (const modulo_int &rhs) const { return modulo_int(*this) /= rhs; }
  constexpr modulo_int &operator /= (const modulo_int &rhs) {
    return (*this) *= ~rhs;
  }
  constexpr bool operator == (const modulo_int &rhs) const {
    return value == rhs();
  }
  constexpr bool operator != (const modulo_int &rhs) const {
    return value != rhs();
  }
  constexpr modulo_int power (unsigned long long pow) const {
    modulo_int result(1), mult(*this);
    while (pow > 0) {
      if (pow & 1) result *= mult;
      mult *= mult;
      pow >>= 1;
    }
    return result;
  }
  friend std::istream &operator >> (std::istream &stream, modulo_int &lhs) {
    stream >> lhs.value;
    lhs.normalize();
    return stream;
  }
  friend std::ostream &operator << (std::ostream &stream, const modulo_int &rhs) {
    return stream << rhs.value;
  }
};

template <class T>
class factorials {
public:
  using value_type = T;

public:
  std::vector<value_type> fact, fact_inv;

  factorials(int size_ = 200000): fact(size_ + 1), fact_inv(size_ + 1) {
    fact[0] = 1;
    for (int i = 1; i <= size_; ++i) {
      fact[i] = fact[i - 1] * value_type(i);
    }
    fact_inv[size_] = ~fact[size_];
    for (int i = size_; i > 0; --i) {
      fact_inv[i - 1] = fact_inv[i] * value_type(i);
    }
  }

  value_type operator () (int n, int r) const {
    return fact[n] * fact_inv[n - r] * fact_inv[r];
  }

};

using modint = modulo_int<std::integral_constant<int, 1000000007>>;
constexpr int mx = 2005;
modint dp[mx * 2][mx * 2];
factorials<modint> fact(mx * 4);

int main() {
  int N;
  std::cin >> N;
  std::vector<int> A(N), B(N);
  for (int i: range(0, N)) {
    std::cin >> A[i] >> B[i];
    dp[mx - A[i]][mx - B[i]] += 1;
  }
  for (int i: range(0, mx * 2)) {
    for (int j: range(0, mx * 2)) {
      if (i > 0) dp[i][j] += dp[i - 1][j];
      if (j > 0) dp[i][j] += dp[i][j - 1];
    }
  }
  modint ans;
  for (int i: range(0, N)) {
    ans += dp[mx + A[i]][mx + B[i]];
    ans -= fact(A[i] * 2 + B[i] * 2, A[i] * 2);
  }
  std::cout << ans / 2 << '\n';
  return 0;
}


Measured memory_bytes: 127616