#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define int long long
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (b); i >= (a); i --)
#define REP(i, a) for (int i = 0; i < (a); ++i)
#define REPD(i, a) for (int i = (a) - 1; i >= 0; --i)
#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)
constexpr ll LINF = (1ll << 60);
constexpr int INF = (1ll << 30);
constexpr int Mod = 1e9 + 7;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
/*
Phu Trong from Nguyen Tat Thanh High School for gifted student
*/
template <class X, class Y>
bool minimize(X &x, const Y &y){
X eps = 1e-9;
if (x > y + eps) {x = y; return 1;}
return 0;
}
template <class X, class Y>
bool maximize(X &x, const Y &y){
X eps = 1e-9;
if (x + eps < y) {x = y; return 1;}
return 0;
}
#define MAX 2505
#define LIM 5005
int nArr;
vector<int> seg;
int l[MAX], r[MAX];
int dp[MAX * 2][MAX];
int inv[MAX];
int power(int a, int exp){
int res = 1;
for (; exp > 0; exp >>= 1, a = (1LL * a * a) % Mod) if(exp & 1){
res = (1LL * res * a) % Mod;
}
return res;
}
void add(int &x, int y){
x += y;
if (x >= Mod) x %= Mod;
while(x < 0) x += Mod;
}
int mul(int x, int y){
return 1LL * x * y % Mod;
}
void process(void){
cin >> nArr;
for (int i = 1; i <= nArr; ++i){
cin >> l[i] >> r[i];
seg.emplace_back(l[i]);
seg.emplace_back(r[i] + 1);
}
seg.emplace_back(0);
sort(seg.begin(), seg.end());
seg.resize(unique(seg.begin(), seg.end()) - seg.begin());
for (int i = 0; i <= nArr; ++i) inv[i] = power(i, Mod - 2);
for (int i = 0; i <= nArr; ++i) dp[0][i] = 1;
int n = (int)seg.size();
for (int i = 1; i < n - 1; ++i){
int x = seg[i + 1] - seg[i];
for (int pos = 0; pos <= nArr; ++pos){
dp[i][pos] = dp[i - 1][pos];
int nCk = 1, cnt = 0;
for (int last = pos; last >= 1; --last){
if (l[last] <= seg[i] && seg[i + 1] - 1 <= r[last]){
++cnt;
nCk = mul(nCk, x + cnt - 1) * inv[cnt] % Mod;
add(dp[i][pos], mul(dp[i - 1][last - 1], nCk));
// add(dp[i][pos], mul(dp[i - 1][last - 1], C[x + cnt - 1][cnt]));
}
}
}
}
/*
C(x + cnt - 1, cnt)
(x + cnt - 1)! / cnt! . (x - 1)!
(x - 1 + 1) * (x - 1 + 2) .. * (x - 1 + cnt) / cnt!
*/
cout << (dp[n - 2][nArr] - 1 + Mod) % Mod;
}
signed main(){
#define name "Whisper"
cin.tie(nullptr) -> sync_with_stdio(false);
// freopen(name".inp", "r", stdin);
// freopen(name".out", "w", stdout);
process();
return (0 ^ 0);
}
