#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define re exit(0);
const int mod = 1e9 + 7;
int n,a[509],b[509];
vector <int> X;
int dp[509][1009],pref[509][1009];
int cnt;
pair <int,int> halfseg[1009];
int main() {
ios_base::sync_with_stdio(0);cin.tie(nullptr);
cin >> n;
for (int i = 1;i <= n;i++) {
cin >> a[i] >> b[i];
X.push_back(a[i] - 1);
X.push_back(b[i]);
}
sort(X.begin(),X.end());
X.resize(unique(X.begin(),X.end()) - X.begin());
for (int i = 0;i < (int)X.size() - 1;i++) {
halfseg[++cnt] = {X[i],X[i + 1]};
}
// for (int i = 1;i <= cnt;i++) cout << halfseg[i].first << " " << halfseg[i].second << '\n';
// cout << '\n';
int res = 0;
for (int i = 1;i <= n;i++) {
for (int j = 1;j <= cnt;j++) {
if (a[i] <= halfseg[j].first + 1 && halfseg[j].second <= b[i]) {
dp[i][j] = halfseg[j].second - halfseg[j].first;
for (int k = i - 1;k >= 1;k--) {
dp[i][j] = (dp[i][j] + 1ll * pref[k][j - 1] * (halfseg[j].second - halfseg[j].first)) % mod;
}
// cout << i << " " << halfseg[j].first + 1 << " " << halfseg[j].second << " " << dp[i][j] << '\n';
}
pref[i][j] = (pref[i][j - 1] + dp[i][j]) % mod;
res = (res + dp[i][j]) % mod;
}
}
cout << res;
}
/*
Aiming:
==
+++++***
+:::::-=*
------=
========== ================== --:--== ============--
========== ==-------=--:=--==== ---==++ ===========--====-=
==--======== ==--================= =:::-=+ ==============----====
==:-========= ===:=== ======= =::--=+ ======== ==--====
==--========== ==-:=== ======= -:::-:= ======= =======
==--:== ======= ==--=== ======= =-:::-= ======= =======
=-.-=== ======= ==-==== ======= *:::----* ======= =======
==--:== ======= ==-================== +-:::::-+ ====== =======
==-:-=== ======= ==--================ *=-:::::-= ======= =======
==---=============== ==--============= +--::---==* ====--= =======
===--================= ==:-=== =:-::::--=+ ====-=== =======
==.-=================== ==--=== =::::::---+ ====---== =========
==---== ======= ======= +-:---=====+ ==-===--==============
======= ======= ======= =-:::::::--=+ =--=-=============
======== ======= ======= =--::::::--=+ =============
***++++++++++*****
*/
