#include "bits/stdc++.h"
using namespace std;
#define for_(i, s, e) for (int i = s; i < (int) e; i++)
#define for__(i, s, e) for (ll i = s; i < e; i++)
typedef long long ll;
typedef vector<int> vi;
typedef array<int, 2> ii;
// #define endl '\n'
const ll mod = 1e9+7;
ll power(ll x, ll y) {
if (y == 0) return 1;
ll p = power(x, y/2) % mod;
p = (p * p) % mod;
return (y%2 == 0)? p : (x * p) % mod;
}
ll modInverse(ll a) {
return power(a, mod-2);
}
const int MXN = 500;
ll choose[4*MXN+2][MXN+1], dp[2][MXN+1][MXN+1][2];
int main() {
#ifdef mlocal
freopen("test.in", "r", stdin);
#endif
ios_base::sync_with_stdio(false);
cin.tie(0);
int n; cin >> n;
vector<ii> lt(n);
vi raw(2*n);
for_(i, 0, n) {
cin >> lt[i][0] >> lt[i][1];
raw[2*i] = lt[i][0], raw[2*i+1] = lt[i][1];
}
sort(raw.begin(), raw.end());
raw.resize(unique(raw.begin(), raw.end()) - raw.begin());
vector<ii> seg;
int pre = -1;
for_(i, 0, raw.size()) {
if (pre < raw[i] and pre != -1) seg.push_back({pre, raw[i]-1});
seg.push_back({raw[i], raw[i]});
pre = raw[i]+1;
}
int ns = seg.size();
memset(choose, 0, sizeof(choose)); memset(dp, 0, sizeof(dp));
for_(i, 0, ns) {
choose[i][0] = 1;
for_(r, 1, min(n, seg[i][1]-seg[i][0]+1) + 1) choose[i][r] = (((choose[i][r-1] * (seg[i][1]-seg[i][0]-r+2)) % mod) * modInverse(r)) % mod;
}
int c = 0;
for (int s = ns-1; s >= 0; s--) {
memset(dp[c], 0, sizeof(dp[c]));
for (int ct = min(n-1, seg[s][1]-seg[s][0]+1); ct >= 0; ct--) {
dp[c][ct][n][0] = choose[s][ct];
for (int idx = n-1; idx >= 0; idx--) {
if (seg[s][0] >= lt[idx][0] and seg[s][1] <= lt[idx][1]) dp[c][ct][idx][1] += dp[c][ct+1][idx+1][0];
if (dp[c][ct][idx][1] >= mod) dp[c][ct][idx][1] -= mod;
dp[c][ct][idx][1] += (choose[s][ct] * (s < ns-1 ? dp[1-c][0][idx][1] : 0)) % mod;
if (dp[c][ct][idx][1] >= mod) dp[c][ct][idx][1] -= mod;
dp[c][ct][idx][0] = (dp[c][ct][idx][1] + dp[c][ct][idx+1][0]) % mod;
}
}
c = 1-c;
}
cout << (dp[1-c][0][0][0]-1+mod) % mod << endl;
}
