#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2")
#define int long long
#define pii pair<int,int>
#define vi vector<int>
#define ff first
#define ss second
#define sp << " " <<
#define all(x) x.begin(),x.end()
#define big(x) ((int)(x.size()))
using namespace std;
const int MOD = 1e9+7, LIM = 2e6+1, inf = 2e9;
int add(int x,int y) {
if ((x + y) >= MOD) return x + y - MOD;
return x + y;
}
int mult(int x,int y) {
return (1LL * x * y) % MOD;
}
int expo(int x,int y) {
if (!y) return 1;
int e = expo(x, y >> 1);
e = mult(e, e);
if (y & 1) e = mult(e, x);
return e;
}
int divide(int x, int y) {
return mult(x, expo(y, MOD - 2));
}
vi f(LIM), finv(LIM);
int nck(int n, int k) {
if (n < k || n < 0 || k < 0) return 0;
return mult(f[n], mult(finv[k], finv[n - k]));
}
void combo() {
f[0] = 1;
for (int i = 1; i < LIM; i++) f[i] = mult(f[i - 1], i);
finv[LIM - 1] = divide(1, f[LIM - 1]);
for (int i = LIM - 2; i >= 0; i--) finv[i] = mult(finv[i + 1], i + 1);
}
int dp[501][1001];
int cfs[501][1001];
void solve() {
combo();
int n;
cin >> n;
vi a(n+1),b(n+1);
vi v;
for (int i=1;i<=n;i++) cin >> a[i] >> b[i];
for (int i=1;i<=n;i++) v.push_back(a[i]);
for (int i=1;i<=n;i++) v.push_back(b[i]+1);
sort(all(v));
vector<pii> ranges;
for (int i=1;i<big(v);i++) if (v[i-1] <= v[i]-1) ranges.push_back({v[i-1],v[i]-1});
if (ranges.empty()) ranges.push_back({a[1],b[1]});
dp[0][0] = 1;
vi inv(n+1);
for (int i=0;i<=n;i++) inv[i] = divide(1,i);
for (int i=1;i<=n;i++) {
for (int j=1;j<=big(ranges);j++) {
pii it = ranges[j-1];
int sel = 1;
for (int p = 1;p<=i;p++) {
sel = mult(sel,it.ss-it.ff+1-p+1);
sel = mult(sel,inv[p]);
cfs[i][j] = add(cfs[i][j],mult(sel,nck(i-1,p-1)));
}
}
}
for (int i=1;i<=n;i++) {
for (int r = 1;r<=big(ranges);r++) {
pii it = ranges[r-1];
if (it.ff >= a[i] && it.ss <= b[i]) {
for (int j = 0;j<i;j++) {
int prvdp = 0;
for (int rp = 0;rp<r;rp++) prvdp = add(prvdp,dp[j][rp]);
dp[i][r] = add(dp[i][r],mult(prvdp,cfs[i-j][r]));
}
}
}
}
int ans = 0;
for (int i = 1;i<=n;i++) for (int j = 1;j<=big(ranges);j++) ans = add(ans,dp[i][j]);
cout << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0);
#ifdef Dodi
freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);
#endif
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
