#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define pii pair<int, int>
#define fi first
#define se second
#define rep(i, a, b) for (int i = a; i <= b; ++i)
#define per(i, b, a) for (int i = b; i >= a; --i)
#define pb push_back
#define all(v) (v).begin(), (v).end()
const int MAXN = 5e2+10;
const int MOD = 1e9+7;
int l[MAXN], r[MAXN], dp[MAXN][2*MAXN], ch[2*MAXN][MAXN], ch2[MAXN][MAXN], ifact[MAXN];
int32_t main() {
ios_base::sync_with_stdio(0);cin.tie(nullptr);
int n;cin >> n;
ifact[0] = ifact[1] = 1;
rep(i,2,n) ifact[i] = MOD-(MOD/i)*ifact[MOD%i]%MOD;
rep(i,1,n) ifact[i] = ifact[i]*ifact[i-1]%MOD;
vector<int> ev;
rep(i,1,n) {
cin >> l[i] >> r[i];
ev.pb(l[i]);
ev.pb(r[i]+1);
}
ev.pb(0);
sort(all(ev));
ev.erase(unique(all(ev)), ev.end());
int m = ev.size()-1;
rep(i,1,m-1) {
ch[i][0] = 1LL;
rep(j,1,n) {
int len = ev[i+1]-ev[i];
ch[i][j] = 1;
per(k,len+j-2,len-1) ch[i][j] = (ch[i][j]*k)%MOD;
ch[i][j] = ch[i][j]*ifact[j-1]%MOD;
}
}
rep(j,0,m)dp[0][j] = 1;
rep(i,1,n) {
dp[i][0] = 1;
rep(j,1,m-1) {
dp[i][j] = (dp[i][j-1]+dp[i-1][j]-dp[i-1][j-1]+MOD)%MOD;
//cout << dp[i][j] << '\n';
int cnt = 1;
if(l[i] > ev[j] || r[i] < ev[j+1]-1) continue;
dp[i][j] = (dp[i][j] + dp[i-1][j-1]*(ev[j+1]-ev[j]))%MOD;
per(k,i-1,1) {
if(l[k] <= ev[j] && r[k] >= ev[j+1]-1) {
cnt++;
dp[i][j] = (dp[i][j] + dp[k-1][j-1]*ch[j][cnt])%MOD;
}
}
//cout << i << ' ' << j << ' ' << dp[i][j] << '\n';
}
}
cout << dp[n][m-1] -1<< '\n';
}
