#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define all(v) v.begin(), v.end()
#define sz(v) (int)v.size()
#define MOO(i, a, b) for(int i=a; i<b; i++)
#define M00(i, a) for(int i=0; i<a; i++)
#define MOOd(i,a,b) for(int i = (b)-1; i >= a; i--)
#define M00d(i,a) for(int i = (a)-1; i>=0; i--)
#define FAST ios::sync_with_stdio(0); cin.tie(0);
#define finish(x) return cout << x << '\n', 0;
#define dbg(x) cerr << ">>> " << #x << " = " << x << "\n";
#define _ << " _ " <<
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef pair<int,int> pi;
typedef pair<ld,ld> pd;
typedef complex<ld> cd;
const ll MOD = 1000000007;
const int MAX_N = 505;
int n;
pi arr[MAX_N];
ll fact[MAX_N];
ll factor[MAX_N*4][MAX_N];
vector<ll> dp[4*MAX_N];
bool cont(pi p1, pi p2) {
return p2.f <= p1.f && p1.s <= p2.s;
}
int len(pi p) {
return p.s - p.f + 1;
}
ll mpow(ll base, ll exp) {
if(exp == 0) return 1;
ll res = mpow(base, exp/2);
res *= res; res %= MOD;
if(exp%2 == 1) {
res *= base; res %= MOD;
}
return res;
}
ll inv(ll k) {
return mpow(k, MOD-2);
}
ll getSum(int j, vector<ll>& v) {
ll res = 0;
int ctr = 0;
M00d(idx, sz(v)) {
if(v[idx] == 0) continue;
ll val = (v[idx] * factor[j][ctr]) % MOD;
res += val;
res %= MOD;
ctr++;
}
return res;
}
int main() { FAST
fact[0] = 1;
MOO(i, 1, MAX_N) fact[i] = (fact[i-1] * i) % MOD;
cin >> n;
M00(i, n) cin >> arr[i].f >> arr[i].s;
vi idxs;
idxs.pb(0);
M00(i, n) {
idxs.pb(arr[i].f);
idxs.pb(arr[i].s);
}
sort(all(idxs));
idxs.erase(unique(all(idxs)), idxs.end());
vector<pi> intervals;
intervals.pb(mp(0,0));
MOO(i, 1, sz(idxs)) {
pi p = mp(idxs[i-1]+1, idxs[i]-1);
if(p.f <= p.s) intervals.pb(p);
intervals.pb(mp(idxs[i], idxs[i]));
}
sort(all(intervals));
M00(i, sz(intervals)) {
ll x = len(intervals[i]);
ll cur = 1;
M00(j, MAX_N-1) {
cur *= x+j; cur %= MOD;
factor[i][j] = (cur * inv(fact[j+1])) % MOD;
}
}
dp[0].pb(1);
MOO(i, 1, sz(intervals)) {
if(cont(intervals[i], arr[0])) dp[i].pb(1);
else dp[i].pb(0);
}
MOO(i, 1, n) {
ll cursum = 0;
M00(j, sz(intervals)) {
ll add = getSum(j, dp[j]);
if(cont(intervals[j], arr[i])) {
dp[j].pb(cursum);
} else {
dp[j].pb(0);
}
cursum += add;
cursum %= MOD;
}
}
ll ans = MOD-1;
M00(i, sz(intervals)) {
ans += getSum(i, dp[i]);
ans %= MOD;
}
finish(ans);
}
