#include <bits/stdc++.h>
using namespace std;
#define int long long
#define stoi stoll
using pii=pair<int,int>;
#define all(c) begin(c),end(c)
#define rall(c) rbegin(c),rend(c)
#define fore(x,c) for(auto &&x:c)
#define rep(i,a,n) for(int i=a,i##len=(int)(n);i<i##len;++i)
#define rrep(i, a, n) for(int i=(int)(n-1);i>=a;--i)
#define sz(c) ((int)c.size())
#define contains(c,x) (c.find(x)!=end(c))
#define inseg(l,x,r) ((l)<=(x)&&(x)<(r))
#define dump(...)
#define pb push_back
#define _ 0
const signed INF_=1001001001; const long long INF=1001001001001001001LL;
const int DX[9]={0,1,0,-1,1,1,-1,-1,0},DY[9]={-1,0,1,0,-1,1,1,-1,0};
template<class T> ostream& operator<<(ostream &os,const vector<T> &v) {
    for (auto i = begin(v); i != end(v); i++) os<<*i<<(i==end(v)-1?"":" ");return os;}
template<class T> istream& operator>>(istream &is,vector<T> &v) {
    for (auto i = begin(v); i != end(v); i++) is>>*i;return is;}
template<class T,class U> istream& operator>>(istream &is, pair<T,U> &p) {
    is>>p.first>>p.second;return is;}
template<class T, class U> bool chmax(T &a,const U &b){return a<b?a=b,1:0;}
template<class T, class U> bool chmin(T &a,const U &b){return a>b?a=b,1:0;}
template <class T> void psum(T& c) {partial_sum(begin(c), end(c), begin(c));}
template<class T> using heap=priority_queue<T,vector<T>,greater<T>>;
struct before_main_function {
    before_main_function() {
        cin.tie(0); ios::sync_with_stdio(0);
        cout << setprecision(15) << fixed;
        // #define endl "\n"
    }
} before_main_function;
//------------------8<------------------------------------8<--------------------

template <int mod>
class ModInt {
public:
    ModInt() : v(0) {}
    ModInt(int x) : v((x+mod)%mod) {}
    int value() const {return v;}
    const ModInt operator+(const ModInt &r) const { return ModInt(this->v + r.v); }
    const ModInt operator-(const ModInt &r) const { return ModInt(this->v + mod - r.v); }
    const ModInt operator*(const ModInt &r) const { return ModInt(this->v * r.v); }
    const ModInt operator/(const ModInt &r) const { return (*this * (~r)); }
    const ModInt operator^(int k) const { return ModInt(bpow(this->v, k)); }
    const ModInt operator~() const { return ModInt(bpow(this->v, mod-2)); }
    bool operator==(const ModInt &r) const { return this->v == r.v; }
    bool operator!=(const ModInt &r) const { return this->v != r.v; }
    ModInt& operator+=(const ModInt &r) { return *this = *this + r; }
    ModInt& operator-=(const ModInt &r) { return *this = *this - r; }
    ModInt& operator*=(const ModInt &r) { return *this = *this * r; }
    ModInt& operator/=(const ModInt &r) { return *this = *this * (~r); }
private:
    int v;
    int bpow(int a, int b) const {
        int ret = 1;
        while (b > 0) {
            if (b & 1) ret = (ret * a) % mod;
            a = (a * a) % mod;
            b >>= 1;
        }
        return ret;
    }
};
using Mint = ModInt<1000000007>;
struct Factorial {
    static constexpr int MAX_N = 2000006;
    vector<Mint> fact, fact_inv;
    Factorial(size_t size = MAX_N) : fact(size), fact_inv(size) {
        fact[0] = fact_inv[0] = 1;
        for (int i = 1; i < MAX_N; ++i) {
            fact[i] = fact[i - 1] * i;
            fact_inv[i] = ~fact[i];
        }
    }
    Mint combination(int N, int R) {
        if (N < R) return 0;
        return fact[N] * fact_inv[N - R] * fact_inv[R];
    }
    static Mint bin_pow(Mint x, int p) {
        if (x.value() == 0) return x;
        Mint prod = 1;
        while (p > 0) {
            if (p & 1) prod *= x;
            x *= x;
            p >>= 1;
        }
        return prod;
    }
};
signed main() {
    int N;
    cin >> N;
    vector<int> A(N), B(N);
    rep(i, 0, N) cin >> A[i] >> B[i];

    vector<vector<Mint>> dp(4200, vector<Mint>(4200));
    rep(i, 0, N) {
        dp[2100-A[i]][2100-B[i]] += 1;
    }
    rep(i, 0, 4190) {
        rep(j, 0, 4190) {
            dp[i + 1][j] += dp[i][j];
            dp[i][j + 1] += dp[i][j];
        }
    }
    
    Factorial fact;
    Mint ans = 0;
    rep(i, 0, N) {
        ans += dp[2100 + A[i]][2100 + B[i]];
        ans -= fact.combination(2 * (A[i] + B[i]), 2 * B[i]);
    }
    ans /= 2;
    cout << ans.value() << endl;
    return (0^_^0);
}



Measured memory_bytes: 172672