#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>
#include <atcoder/modint>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

using mint = atcoder::modint1000000007;

ostream& operator<<(ostream& os, const mint& m){
    os << m.val();
    return os;
}

template<typename T>
class Compress{
    public:
    vector<T> data;
    int offset;
    Compress(vector<T> data_, int offset=0): offset(offset){
        data = data_;
        sort(begin(data), end(data));
        data.erase(unique(begin(data), end(data)), end(data));
    };
    int operator[](T x) {
        auto p = lower_bound(data.begin(), data.end(), x);
        assert(x == *p);
        return offset+(p-data.begin());
	}
    T inv(int x){
        return data[x-offset];
    }
    int size(){
        return data.size();
    }
};

template<typename T>
class CumsumGrid{
    public:
    CumsumGrid(vector<vector<T>> v): v(v){
        n = v.size();
        m = v[0].size();
        v_cumsum = vector<vector<T>>(n+1, vector<T>(m+1, T(0)));
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < m; j++){
                v_cumsum[i+1][j+1] = v_cumsum[i+1][j]+v_cumsum[i][j+1]-v_cumsum[i][j]+v[i][j];
            }
        }
    }
    /**
     * sum(v[il:ir)[jl:jr))
     */ 
    T sum(int il, int ir, int jl, int jr){
        if(ir <= il) return T(0);
        if(jr <= jl) return T(0);
        if(ir > n) ir = n;
        if(jr > m) jr = m;
        if(il < 0) il = 0;
        if(jl < 0) jl = 0;
        return v_cumsum[ir][jr]-v_cumsum[ir][jl]-v_cumsum[il][jr]+v_cumsum[il][jl];
    }
    private:
    int n, m;
    vector<vector<T>> v;
    vector<vector<T>> v_cumsum;
};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int n; cin >> n;
    vector<int> a(n), b(n);
    vector<int> v;
    for(int i = 0; i < n; i++){
        cin >> a[i] >> b[i];
        v.push_back(a[i]);
        v.push_back(b[i]);
    }
    auto cp = Compress<int>(v);
    vector<mint> proba(n+1);
    proba[1] = 1;
    vector<mint> f = {mint(1)};
    for(int len = 2; len <= n; len++){
        vector<mint> fs = {mint(0)};
        for(int i = 0; i < f.size(); i++){
            fs.push_back(f[i]/(i+1));
        }
        if(len%2 == 0){
            // 前より大きい
            // f(0) = 0になっている
            f = fs;
        }else{
            // 前より小さい
            mint f1 = accumulate(fs.begin(), fs.end(), mint(0));
            for(int i = 0; i < fs.size(); i++) fs[i] *= -1;
            fs[0] += f1;
            f = fs;
        }
        for(int i = 0; i < f.size(); i++){
            proba[len] += f[i]/(i+1);
        }
    }
    int m = cp.size();
    auto dp = vec3d(n, m-1, n+1, mint(0));
    for(int j = 0; j < m-1; j++){
        int l = cp.data[j], r = cp.data[j+1];
        if(r <= a[0] || l >= b[0]) continue;
        mint p = mint(r-l)/mint(b[0]-a[0]);
        dp[0][j][1] = p;
    }
    for(int i = 1; i < n; i++){
        auto v = dp[i-1];
        for(int j = 0; j < m-1; j++){
            for(int k = 0; k <= n; k++){
                v[j][k] *= proba[k];
            }
        }
        auto cumsum = CumsumGrid<mint>(v);
        for(int j = 0; j < m-1; j++){
            int l = cp.data[j], r = cp.data[j+1];
            if(r <= a[i] || l >= b[i]) continue;
            mint p = mint(r-l)/mint(b[i]-a[i]);
            // 同じ所
            for(int k = 1; k <= n; k++){
                dp[i][j][k] += dp[i-1][j][k-1]*p;
            }
            // 違う場所
            if(i%2 == 0){
                // 小さくなる
                dp[i][j][1] += cumsum.sum(j+1, m, 0, n+1)*p;
            }else{
                // 大きくなる
                dp[i][j][1] += cumsum.sum(0, j, 0, n+1)*p;
            }
        }

    }
    mint ans = 0;
    for(int j = 0; j < m-1; j++){
        for(int k = 1; k <= n; k++){
            ans += dp[n-1][j][k]*proba[k];
        }
    }
    cout << ans << endl;
}