#include <bits/stdc++.h>
using namespace std;
void just_do_it();
int main() {
#ifdef KAMIRULEZ
freopen("kamirulez.inp", "r", stdin);
freopen("kamirulez.out", "w", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(0);
just_do_it();
return 0;
}
const int maxn = 5e2 + 20;
const long long mod = 1e9 + 7;
bool flag[maxn];
long long inv[maxn];
long long fact_inv[maxn];
long long cur[maxn];
long long nxt[maxn];
pair<int, int> events[maxn * 2];
int n;
void trans() {
for (int i = 1; i <= n; i++) {
if (flag[i]) {
nxt[i] = cur[i] + 1;
if (nxt[i] >= mod) {
nxt[i] -= mod;
}
}
else {
nxt[i] = cur[i];
}
}
for (int i = 1; i <= n; i++) {
for (int j = i + 1; j <= n; j++) {
if (flag[j]) {
nxt[j] += cur[i];
if (nxt[j] >= mod) {
nxt[j] -= mod;
}
}
}
}
swap(cur, nxt);
}
void shift(int len) {
for (int i = 1; i <= n; i++) {
if (flag[i]) {
nxt[i] = (cur[i] + len) % mod;
}
else {
nxt[i] = cur[i];
}
}
for (int i = 1; i <= n; i++) {
int cnt = 0;
long long num = 1;
for (int j = i + 1; j <= n; j++) {
if (flag[j]) {
cnt++;
num = num * (len + cnt - 1) % mod;
if (flag[i]) {
nxt[j] = (nxt[j] + cur[i] * num % mod * fact_inv[cnt] % mod + num * (len - 1) % mod * fact_inv[cnt + 1] % mod) % mod;
}
else {
nxt[j] = (nxt[j] + cur[i] * num % mod * fact_inv[cnt] % mod) % mod;
}
}
}
}
swap(cur, nxt);
}
void just_do_it() {
inv[1] = 1;
fact_inv[0] = 1;
fact_inv[1] = 1;
for (int i = 2; i < maxn; i++) {
inv[i] = (mod - mod / i) * inv[mod % i] % mod;
fact_inv[i] = fact_inv[i - 1] * inv[i] % mod;
}
cin >> n;
for (int i = 1; i <= n; i++) {
int a, b;
cin >> a >> b;
events[i * 2 - 1] = make_pair(a, i);
events[i * 2] = make_pair(b + 1, -i);
}
sort(events + 1, events + n * 2 + 1);
int cur_t = 0;
for (int i = 1; i <= n * 2; i++) {
int nxt_t = events[i].first;
int id = events[i].second;
bool begin_t = (i == 1 || events[i].first != events[i - 1].first);
bool end_t = (i == n * 2 || events[i].first != events[i + 1].first);
if (begin_t) {
if (cur_t < nxt_t - 1) {
shift(nxt_t - 1 - cur_t);
cur_t = nxt_t - 1;
}
}
if (id > 0) {
flag[id] = true;
}
else {
flag[-id] = false;
}
if (end_t && cur_t == nxt_t - 1) {
trans();
cur_t = nxt_t;
}
}
long long res = 0;
for (int i = 1; i <= n; i++) {
res += cur[i];
res %= mod;
}
cout << res;
}
