/*
Telebe of Adicto && Mamedov yani AzeTurk810
I see humans but no humanity
*/
#include <algorithm>
#include <array>
#include <iostream>
#include <map>
#include <unordered_map>
#include <vector>
// mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
using ll = long long;
using namespace std;
#define ln '\n'
#define INFi 1e9
#define INFll 1e18
#define map unordered_map
#ifdef ONPC
#include <algo.hpp>
#else
#define dbg(...)
#define dbg_out(...)
#endif
constexpr ll MOD = 1e9 + 7, N = 505, M = N * 4;
int _n, _m;
vector<array<ll, 2>> V;
ll ans;
long long bp(long long a, long long b) {
long long res = 1;
while (b > 0) {
if (b & 1LL)
res = (res * a) % MOD;
a = (a * a) % MOD;
b >>= 1;
}
return res;
}
inline void systemd() {
V.resize(_n);
}
inline ll add(ll l, ll r) {
l += r;
while (l >= MOD) {
l -= MOD;
}
return l;
}
vector<ll> compsf;
map<ll, ll> compr, rev;
int compress() {
sort(compsf.begin(), compsf.end());
compsf.erase(unique(compsf.begin(), compsf.end()), compsf.end());
ll nxt = 0;
for (const ll &v : compsf) {
rev[nxt] = v;
compr[v] = nxt++;
}
return compsf.size();
}
char solve() {
if (!(cin >> _n))
return 1;
systemd();
for (auto &[a, b] : V) {
cin >> a >> b;
compsf.push_back(a);
// compsf.push_back(a - 1);
compsf.push_back(b);
// compsf.push_back(b - 1);
}
_m = compress();
vector<vector<ll>> dp(_m, vector<ll>(_m, 0));
for (size_t k = 0; k < _n; k++) {
int ci = compr[V[k][0]], cj = compr[V[k][1]];
int ai = V[k][0], bi = V[k][1];
dp[ci][cj] = bi - ai + 1;
for (int i = 0; i < _n; i++) {
for (int j = i; j < _n; j++) {
ll aj = V[i][0], bj = V[j][1];
if (aj > bj)
continue;
ll ca = compr[aj], cb = compr[bj];
ll wj = dp[ca][cb];
if (aj >= bi)
continue;
if (bj < ai) {
dp[ci][cj] = add(wj, dp[ci][cj]);
}
}
}
ans = add(ans, dp[ci][cj]);
dbg(dp[ci][cj]);
dbg("______");
}
for (size_t i = 0; i < _m; i++) {
dbg(dp[i]);
}
cout << ans << ln;
return 0;
}
// Attack on titan<3
signed main() {
ios::sync_with_stdio(0);
cin.tie(nullptr);
int t = 1e9;
// cin >> t;
for (int cases = 0; cases < t; cases++) {
if (solve())
break;
#ifdef ONPC
cerr << "__________\n";
#endif
}
}
// Just Imaginary
/*
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣀⣀⠀⠀⠀⢀⣴⣾⠀⠀⠀⡀⢀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢸⣿⣿⣿⣦⣾⣿⣿⣿⣿⣿⡆⠁⠀⢀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠹⣿⣿⣿⣿⣿⣿⣿⣿⡿⠁⠀⡠⠂⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⣀⠠⠔⠚⣿⣿⣿⣿⣿⣦⡄⠀⠁⠀⠀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⢀⠠⠐⢂⠉⡀⣀⣤⣄⢻⣿⣿⡟⢈⡹⣿⡀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⡀⠄⠂⠈⠀⣶⣤⣾⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠘⣷⡀⠀⡀⠐⠂⠐⢄
⠀⠀⠀⠀⠀⠀⠀⣿⣿⠟⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣧⣀⣾⣷⠯⠀⠤⠤⠄⠈
⠀⠀⠀⠀⠀⠀⣼⣿⡟⠀⠀⣹⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⣄⡀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⣰⣿⠋⠀⠀⢠⣾⣿⣿⣿⣿⣿⣭⠟⢻⣿⣿⣿⣿⡿⠁⠀⠀⠀⠀
⠀⠀⠀⣀⣶⡟⠁⠀⢾⣶⣿⠟⠉⠈⢻⣿⣿⣿⣦⣜⠀⠛⠛⠿⠁⠀⠀⠀⠀⠀
⠚⠻⠿⠿⡿⠁⠀⢠⣿⣿⠁⠀⣠⠖⠋⠉⠻⣿⣿⣿⣶⡀⠀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⠀⠀⠀⠀⣰⣿⡿⠃⠠⠊⠁⠀⠀⠀⠀⠈⢿⣿⣿⠟⠀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⠀⠀⢀⣴⡿⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠘⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀
⠀⠀⠀⣠⣾⠏⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢀⣴⠾⠟⠛⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
*/
