#include<bits/stdc++.h>
#define taskname "A"
using namespace std;
const int lim = 505;
const int LIM = 1e9 + 5;
const int mod = 1e9 + 7;
void add(int& a, int b){
if((a += b) >= mod){
a -= mod;
}
}
int n, a[lim], b[lim];
namespace sub12{
map<int, int>bit;
void update(int p, int x){
for(; p < LIM; p += p & -p){
add(bit[p], x);
}
}
int get(int p){
int ans = 0;
for(; p > 0; p -= p & -p){
auto it = bit.find(p);
if(it != bit.end()){
add(ans, it->second);
}
}
return ans;
}
void solve(){
update(1, 1);
for(int i = 1; i <= n; i++){
for(int j = b[i]; j >= a[i]; j--){
update(j + 1, get(j));
}
}
cout << (get(LIM - 1) + mod - 1) % mod;
}
}
namespace sub34{
int power(int a, int b){
int ans = 1;
for(; b > 0; b >>= 1, a = 1LL * a * a % mod){
if(b & 1){
ans = 1LL * ans * a % mod;
}
}
return ans;
}
int inv_gt[lim], pre_Ckn[lim << 1][lim], f[lim][lim << 1];
vector<pair<int, int>>range(1, make_pair(0, 0));
void solve(){
for(int i = inv_gt[0] = 1; i < lim; i++){
inv_gt[i] = 1LL * inv_gt[i - 1] * i % mod;
}
inv_gt[lim - 1] = power(inv_gt[lim - 1], mod - 2) % mod;
for(int i = lim - 2; i > 1; i--){
inv_gt[i] = 1LL * inv_gt[i + 1] * (i + 1) % mod;
}
map<int, int>cnt;
for(int i = 1; i <= n; i++){
cnt[a[i]]++;
cnt[b[i] + 1]--;
}
int sum = 0, pre = 0;
for(auto& [u, v] : cnt){
if(sum > 0){
range.emplace_back(pre, u - 1);
}
sum += v;
pre = u;
}
int N = range.size();
for(int i = 1; i < N; i++){
int len = pre_Ckn[i][1] = range[i].second - range[i].first + 1;
vector<int>cnt_mask(n + 1, pre_Ckn[i][0] = 0);
cnt_mask[0] = 1;
for(int j = 1; j <= n; j++){
pre_Ckn[i][j + 1] = len;
for(int k = min(j, len - 1); k > 0; k--){
add(cnt_mask[k], cnt_mask[k - 1]);
}
for(int k = 1, num = len; k <= min(j, len - 1); k++){
add(pre_Ckn[i][j + 1], 1LL * cnt_mask[k] * (num = 1LL * num * (len - k) % mod) % mod * inv_gt[k + 1] % mod);
}
}
}
memset(f, -1, sizeof(f));
function<int(int, int)>dp;
dp = [&] (int i, int j){
if(min(i, j) == 0){
return 1;
}
int& ans = f[i][j];
if(ans != -1){
return ans;
}
ans = ((dp(i, j - 1) + dp(i - 1, j)) % mod - dp(i - 1, j - 1) + mod) % mod;
if(range[j].first >= a[i] && range[j].second <= b[i]){
for(int k = i, cnt = 0; k > 0; k--){
if(range[j].first >= a[k] && range[j].second <= b[k]){
add(ans, 1LL * (pre_Ckn[j][++cnt] - pre_Ckn[j][cnt - 1] + mod) * dp(k - 1, j - 1) % mod);
}
}
}
return ans;
};
cout << (dp(n, N - 1) + mod - 1) % mod;
}
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
if(fopen(taskname".inp", "r")){
freopen(taskname".inp", "r", stdin);
}
cin >> n;
for(int i = 1; i <= n; i++){
cin >> a[i] >> b[i];
}
int sum = 0;
for(int i = 1; i <= n; i++){
if((sum += b[i] - a[i]) > 1000000){
break;
}
}
if(sum < 1000001){
sub12::solve();
}
else{
sub34::solve();
}
}
