#include <bits/stdc++.h>
#define pb push_back
#define pii pair<ll, ll>
#define nyan "(=^･ω･^=)"
#define read_input freopen("in.txt","r", stdin)
#define print_output freopen("out.txt","w", stdout)
typedef long long ll;
typedef long double ld;
using namespace std;
const ll mod = 1e9+7, maxn = 1e3+10;
ll l[maxn], r[maxn];
ll dp[maxn][maxn], sum[maxn][maxn];
ll ncr[maxn][maxn], inv[maxn];
vector<pii> edit;
vector<ll> v;
ll bigmod(ll a, ll b) {
if(b == 0) return 1;
ll x = bigmod(a, b/2);
x = (x * x) % mod;
if(b & 1) x = (x * a) % mod;
return x;
}
int main()
{
ll n; cin >> n;
for(ll i = 1; i <= n; i++) {
cin >> l[i] >> r[i];
v.pb(l[i]); v.pb(r[i]+1);
}
sort(v.begin(), v.end());
v.erase(unique(v.begin(), v.end()), v.end());
edit.pb({0, 0});
for(ll i = 0; i < (ll)v.size()-1; i++) {
edit.pb({v[i], v[i+1]-1});
}
ll m = edit.size() - 1;
for(ll i = 1; i <= n; i++) inv[i] = bigmod(i, mod-2);
dp[0][0] = 1;
for(ll i = 0; i <= m; i++) sum[0][i] = 1;
for(ll i = 1; i <= n; i++) {
for(ll j = 1; j <= m; j++) {
ll L = edit[j].second - edit[j].first + 1;
ll cnt = 1, mul = L;
if(!(l[i] <= edit[j].first && r[i] >= edit[j].second)) continue;
for(ll k = i-1; k >= 0; k--) {
dp[i][j] = (dp[i][j] + mul * sum[k][j-1]) % mod;
if(l[k] <= edit[j].first && r[k] >= edit[j].second) {
cnt++;
mul = (mul * (L + cnt - 1)) % mod;
mul = (mul * inv[cnt]) % mod;
}
}
}
for(ll j = 1; j <= m; j++)
sum[i][j] = (sum[i][j-1] + dp[i][j]) % mod;
}
ll ans = 0;
for(ll i = 1; i <= n; i++) {
for(ll j = 1; j <= m; j++)
ans = (ans + dp[i][j]) % mod;
}
cout << ans << endl;
return 0;
}
