//Pantyhose(black) + glasses = infinity
#include <bits/stdc++.h>
using namespace std;
#define debug(x) cerr << #x << " = " << x << '\n';
#define BP() cerr << "OK!\n";
#define PR(A, n) {cerr << #A << " = "; for (int _=1; _<=n; ++_) cerr << A[_] << ' '; cerr << '\n';}
#define PR0(A, n) {cerr << #A << " = "; for (int _=0; _<n; ++_) cerr << A[_] << ' '; cerr << '\n';}
#define FILE_NAME "boat"
const int MAX_N = 1002;
const int MOD = 1000000007;
int n, l[MAX_N], r[MAX_N];
vector<pair<int, int> > seg;
int64_t C1[MAX_N][MAX_N], C2[MAX_N][MAX_N];
int64_t inv[MAX_N], inv_fact[MAX_N], f[MAX_N][MAX_N], P[MAX_N][MAX_N];
void read_input() {
cin >> n;
for (int i=1; i<=n; ++i)
cin >> l[i] >> r[i];
}
void init() {
vector<int> x;
for (int i=1; i<=n; ++i) {
x.push_back(l[i]);
x.push_back(r[i]+1);
}
sort(x.begin(), x.end());
x.resize(unique(x.begin(), x.end()) - x.begin());
seg.push_back({0, 0});
for (int i=0; i+1<x.size(); ++i) {
seg.push_back({x[i], x[i+1]-1});
// cerr << seg.back().first << ' ' << seg.back().second << '\n';
}
inv[1] = 1;
inv_fact[0] = inv_fact[1] = 1;
for (int i=2; i<=n; ++i) {
inv[i] = MOD - MOD/i*inv[MOD%i]%MOD;
inv_fact[i] = inv_fact[i-1] * inv[i] % MOD;
}
// debug(inv[2]*2%MOD);
}
int64_t comb(int n, int k) {
if (n<0 || n<k)
return 0;
int64_t res = 1;
for (int i=n-k+1; i<=n; ++i)
res = res * i % MOD;
return res * inv_fact[k] % MOD;
}
bool contain(int u, int v, int l, int r) {
return (u<=l && r<=v);
}
void dp() {
for (int i=1; i<seg.size(); ++i) {
for (int j=1; j<=n; ++j)
C2[i][j] = comb(seg[i].second - seg[i].first + 1, j);
}
for (int i=0; i<=n; ++i)
C1[i][i] = C1[i][0] = 1;
for (int i=1; i<=n; ++i) {
for (int j=1; j<i; ++j)
C1[i][j] = (C1[i-1][j] + C1[i-1][j-1]) % MOD;
}
for (int i=1; i<seg.size(); ++i) {
for (int k=1; k<=n; ++k) {
for (int j=1; j<=k; ++j)
P[i][k] = (P[i][k] + C2[i][j] * C1[k-1][j-1]) % MOD;
}
}
// debug(P[1][1]);
for (int i=0; i<seg.size(); ++i)
f[0][i] = 1;
for (int i=0; i<=n; ++i)
f[i][0] = 1;
int64_t res = 0;
for (int i=1; i<=n; ++i) {
for (int j=1; j<seg.size(); ++j) {
f[i][j] = f[i][j-1];
int cnt = 0;
for (int k=i; k>=1; --k) {
if (contain(l[k], r[k], seg[j].first, seg[j].second)) {
++cnt;
// if (i==3 && j==1 && k==1)
// debug(tmp);
f[i][j] = (f[i][j] + f[k-1][j-1] * P[j][cnt]) % MOD;
}
}
}
}
// debug(f[3][0]);
cout << (f[n][seg.size()-1] - 1 + MOD) % MOD;
}
int main() {
#ifdef GLASSES_GIRL
freopen(FILE_NAME".in", "r", stdin);
freopen(FILE_NAME".out", "w", stdout);
#endif
ios::sync_with_stdio(0); cin.tie(0);
read_input();
init();
dp();
}
