#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define repd(i, a, b) for (int i = (a) - 1; i >= b; i--)
#define pb push_back
#define fi first
#define se second
#define sz(a) ((int)a.size())
typedef long long ll;
const int mod = 1e9 + 7;
const int maxn = 1e3 + 5;
int n, a[maxn], b[maxn];
ll precal[maxn][maxn], inv[maxn];
map<int, int> mm;
ll dp[maxn][maxn], f[maxn];
vector<ll> vi;
ll power_mod(ll a, ll b) {
ll res = 1;
while (b) {
if (b % 2) res = res * a % mod;
a = a * a % mod;
b >>= 1;
}
return res;
}
int main() {
rep(i, 1, maxn) {
inv[i] = power_mod(i, mod - 2);
}
cin >> n;
// mm[0];
rep(i, 0, n) {
cin >> a[i] >> b[i];
mm[a[i] - 1]++;
mm[b[i]]++;
}
int cnt = 0;
for (auto it = mm.begin(); it != mm.end(); it++) {
it->se = cnt++;
vi.pb(it->fi);
}
rep(i, 1, sz(vi)) {
int range = vi[i] - vi[i - 1];
if (range < 2) continue;
rep(j, 1, n + 1) {
// if (j > range) {
// precal[i][j] = precal[i][j - 1];
// continue;
// }
ll cur1 = 1; // Cij
ll cur2 = (ll) range * (range - 1) / 2; // Cirange
cur2 %= mod;
ll res = cur1 * cur2 % mod;
int tar = min(range - 2, j - 2);
rep(k, 1, tar + 1) {
cur1 = cur1 * (ll) (j - k - 1) % mod * inv[k] % mod;
cur2 = cur2 * (ll) (range - k - 1) % mod * inv[k + 2] % mod;
res = (res + cur1 * cur2 % mod) % mod;
}
precal[i][j] = res;
}
}
// cout << precal[3][3] << ' ' << precal[3][2] << endl;
ll ans = 0;
rep(i, 0, n) {
int hi = mm[b[i]] + 1;
int lo = mm[a[i] - 1] + 1;
dp[i][0] = 1; // ntc
repd(k, hi, lo) {
ll ways = (vi[k] - vi[k - 1]) * (i ? dp[i - 1][k - 1] : 1) % mod;
int tot = 1;
repd(j, i, 0) {
if (b[j] < vi[k - 1] + 1 || a[j] > vi[k]) continue;
tot++;
// cout << i << ' ' << k << ' ' << vi[k] - vi[k - 1] << ' ' << tot << endl;
ways += (((j ? dp[j - 1][k - 1] : 1) * precal[k][tot]) % mod);
ways %= mod;
}
// cout << i << ' ' << k << ' ' << ways << endl;
dp[i][k] = ways;
}
rep(k, 1, cnt) {
dp[i][k] = (dp[i][k] + f[k]) % mod;
// if (i == 2) cout << f[k] << endl;
f[k] = dp[i][k];
dp[i][k] = (dp[i][k] + dp[i][k - 1]) % mod;
ans = dp[i][k];
}
}
// cout << ans << endl;
cout << ((ans - 1 + mod) % mod) << '\n';
return 0;
}
