#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define srt(x) sort(all(x))
#define sz(x) (ll)(x.size())
#define pii pair < int, int >
#define pll pair < ll, ll >
#define debug(x) cerr << (#x) << " = " << (x) << endl
const int mod = 1e9 + 7;
const int N = 1001;
const ll OO = 1e18;
template<typename T>
bool umn (T &fi, T se) { return fi > se ? (fi = se, 1) : 0; }
template<typename T>
bool umx (T &fi, T se) { return fi < se ? (fi = se, 1) : 0; }
int a[N], b[N], fac[N], rfac[N];
int dp[N][N];
int mul (int x, int y) {
return 1ll * x * y % mod;
}
int add (int x, int y) {
x += y;
if (x >= mod)
x -= mod;
return x;
}
int power (int x, int y) {
if (!y)
return 1;
if (y % 2)
return mul(power(x, y - 1), x);
int t = power(x, y / 2);
return mul(t, t);
}
void slv () {
int n;
cin >> n;
vector < int > v;
for (int i = 1; i <= n; ++i) {
cin >> a[i] >> b[i];
v.pb(a[i] - 1);
v.pb(b[i]);
}
sort(all(v));
v.erase(unique(all(v)), v.end());
// return;
int ans = 0;
for (int i = 1; i <= n; ++i) {
for (int j = 1; j < sz(v); ++j) {
int l = v[j - 1] + 1, r = v[j];
int cnt = 0;
if (!(a[i] <= l && r <= b[i]))
continue;
int top = 1;
for (int k = i; k > 0; --k) {
int o = (a[k] <= l && r <= b[k]);
if (o) {
if (r - l + 1 <= cnt) break;
top = mul(top, r - l + 1 - cnt);
cnt++;
dp[i][j] = add(dp[i][j], mul(top, rfac[cnt]));
}
dp[i][j] = add(dp[i][j], mul(dp[k - 1][j - 1], mul(top, rfac[cnt])));
// dp[i][j] += (dp[k - 1][j - 1] + 1) * C(r - l + 1, cnt);
}
// cout << l << " " << r << "\n" << dp[i][j] << "\n";
}
for (int j = 1; j < sz(v); ++j) {
dp[i][j] = add(dp[i][j], dp[i][j - 1]);
}
ans = add(ans, dp[i][sz(v) - 1]);
// cout << dp[i][sz(v) - 1] << "\n";
}
cout << ans;
}
signed main () {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
fac[0] = 1;
for (int i = 1; i < N; ++i)
fac[i] = mul(i, fac[i - 1]);
rfac[N - 1] = power(fac[N - 1], mod - 2);
for (int i = N - 1; i > 0; --i) {
rfac[i - 1] = mul(rfac[i], i);
}
int test = 1;
// cin >> test;
while (test--) {
slv();
cout << "\n";
}
}
