#define Name Spy007
#include <bits/stdc++.h>
#define task "DL"
#define FOR(i,a,b) for (int i=(a),_b=(b);i<=_b;++i)
#define FOD(i,a,b) for (int i=(a),_b=(b);i>=_b;--i)
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define All(x) x.begin(),x.end()
#define sz(x) (int)x.size()
#define fast ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define ll long long
#define endl '\n'
#define PI 3.14159265
using namespace std;
typedef pair <int,int> ii;
typedef pair <int,ii> iii;
typedef pair <int,ll> ill;
typedef pair <ll,ll> lll;
typedef vector <int> vi;
typedef vector <ii> vii;
typedef vector <vi> vvi;
const int nmax = 500;
const ll mod = 1e9 + 7;
int n, m;
ll inv[nmax + 5], g[2 * nmax + 5][nmax + 5], c[nmax + 5][nmax + 5], dp[nmax + 5][2 * nmax + 5];
ii a[nmax + 5];
vi val;
ll Pow(ll a, ll b)
{
if (b == 1) return a % mod;
ll tmp = Pow(a, b / 2);
tmp = (tmp * tmp) % mod;
if (b & 1) return (tmp * a) % mod;
else return tmp;
}
vi Treat(vi val)
{
sort(All(val));
vi ans;
ans.pb(val[0]);
FOR(i, 1, sz(val) - 1)
if (val[i] != val[i - 1]) ans.pb(val[i]);
return ans;
}
void Prep(void)
{
val = Treat(val);
FOR(i, 1, n) inv[i] = Pow(i, mod - 2);
FOR(i, 1, n)
{
c[i][0] = 1;
FOR(j, 1, i)
c[i][j] = (c[i - 1][j - 1] + c[i - 1][j]) % mod;
}
m = sz(val);
FOR(i, 1, m - 1)
{
int len = val[i] - val[i - 1];
g[i][0] = 1;
FOR(j, 1, n)
g[i][j] = (g[i][j - 1] * (((j + len - 1) * inv[j]) % mod)) % mod;
}
}
void Input(void)
{
cin >> n;
FOR(i, 1, n)
{
cin >> a[i].fi >> a[i].se;
val.pb(a[i].fi - 1);
val.pb(a[i].se);
}
}
void Solve(void)
{
Prep();
ll res = 0;
FOR(i, 0, m - 1) dp[0][i] = 1;
FOR(i, 1, n)
{
FOR(j, 1, m - 1)
{
if (a[i].fi <= val[j - 1] + 1 && val[j] <= a[i].se)
{
int cnt = 0;
FOD(k, i, 1)
{
if (a[k].fi <= val[j - 1] + 1 && val[j] <= a[k].se) cnt++;
dp[i][j] = (dp[i][j] + dp[k - 1][j - 1] * g[j][cnt]) % mod;
}
res = (res + dp[i][j]) % mod;
}
dp[i][j] = (dp[i][j] + dp[i][j - 1]) % mod;
}
}
cout << res << endl;
}
signed main()
{
fast;
if (fopen(task".inp","r"))
{
freopen(task".inp","r",stdin);
freopen(task".out","w",stdout);
}
Input();
Solve();
return 0;
}
