#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
constexpr int mod = 1e9 + 7;
constexpr int add(int a, int b) {
return a + b < mod ? a + b : a + b - mod;
}
constexpr int sub(int a, int b) {
return a < b ? a - b + mod : a - b;
}
constexpr int mul(int a, int b) {
return i64(a) * b % mod;
}
constexpr int pow(int x, int n) {
int ret = 1;
for (; n; n >>= 1) {
if (n & 1) ret = mul(ret, x);
x = mul(x, x);
}
return ret;
}
auto sol = [](int n, auto l, auto r) {
vector c(0, 0);
for (int i = 0; i < n; i++) {
c.push_back(l[i]);
c.push_back(r[i] + 1);
}
sort(c.begin(), c.end());
c.erase(unique(c.begin(), c.end()), c.end());
vector d(n + 1, 1);
for (int i = 1; i <= n; i++) d[n] = mul(d[n], i);
d[n] = pow(d[n], mod - 2);
for (int i = n; i >= 1; i--) d[i - 1] = mul(d[i], i);
for (int i = 0; i <= n / 2; i++) d[n - i] = d[i] = mul(d[i], d[n - i]);
vector f(n + 1, 0);
vector s(n + 2, 1);
auto calc = [&](int x) {
if (x <= n) return f[x];
for (int i = n; i >= 0; i--) s[i] = mul(s[i + 1], x - i);
int ret = 0;
int acc = 1;
for (int i = 0; i <= n; i++) {
int val = mul(mul(f[i], d[i]), mul(acc, s[i + 1]));
acc = mul(acc, sub(x, i));
if ((n - i) % 2 == 0) ret = add(ret, val);
else ret = sub(ret, val);
}
return ret;
};
int m = c.size() - 1;
vector dp(m * (n + 1), 0);
for (int iter = 0; iter < n; iter++) {
int acc = 1;
for (int i = 0; c[i] <= r[iter]; i++) {
f[0] = dp[i * (n + 1)];
for (int j = 1; j <= n; j++) f[j] = add(f[j - 1], dp[i * (n + 1) + j]);
if (c[i] >= l[iter]) {
int val = acc;
for (int j = 0; j <= n; j++) {
int prv = dp[i * (n + 1) + j];
dp[i * (n + 1) + j] = add(dp[i * (n + 1) + j], val);
val = add(val, prv);
}
}
acc = add(acc, calc(c[i + 1] - c[i] - 1));
}
}
int ret = 0;
for (int i = 0; i < m; i++) {
f[0] = dp[i * (n + 1)];
for (int j = 1; j <= n; j++) f[j] = add(f[j - 1], dp[i * (n + 1) + j]);
ret = add(ret, calc(c[i + 1] - c[i] - 1));
}
return ret;
};
int main() {
cin.tie(0)->sync_with_stdio(0);
int n; cin >> n;
vector l(n, 0), r(n, 0);
for (int i = 0; i < n; i++) cin >> l[i] >> r[i];
cout << sol(n, l, r) << '\n';
}
