#include <bits/stdc++.h>
#define FOR(i, a, b) for (int i = a, _b = b; i <= _b; ++i)
#define FORD(i, a, b) for (int i = a, _b = b; i >= _b ; --i)
#define REP(i, a) for (int i = 0, _a = a; i < a; ++i)
#define pp pair<int, int>
#define bit(S, i) (((S) >> i) & 1)
#define next __next
#define prev __prev
#define N 1000100
#define NN 1111
#define taskname ""
using namespace std;
int n, a[NN], b[NN], len[NN];
vector<int> exist;
long long rev[N];
const long long MOD = 1e9 + 7;
long long c[NN][NN], dp[NN][NN], clen[NN][NN], g[NN][NN], total[NN][NN];
void Add(long long &a, long long b) { a += b; if (a >= MOD) a -= MOD; }
int main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> n;
FOR(i, 1, n) {
cin >> a[i] >> b[i]; b[i]++;
exist.push_back(a[i]);
exist.push_back(b[i]);
}
sort(exist.begin(), exist.end());
exist.resize(unique(exist.begin(), exist.end()) - exist.begin());
rev[0] = rev[1] = 1;
FOR(i, 2, n) rev[i] = (MOD - (MOD / i) * rev[MOD % i] % MOD) % MOD;
int sz = exist.size() - 1;
FOR(i, 0, n) c[0][i] = 1;
FOR(i, 1, n) {
c[i][i] = 1;
FOR(j, i + 1, n) c[i][j] = (c[i - 1][j - 1] + c[i][j - 1]) % MOD;
// c[k][n]
}
FOR(i, 1, sz) {
len[i] = exist[i] - exist[i - 1];
clen[i][0] = 1;
FOR(j, 1, n) {
g[i][j] = 0;
clen[i][j] = clen[i][j - 1] * (len[i] - j + 1) % MOD * rev[j] % MOD;
}
FOR(k, 2, n) {
g[i][k] = 0;
FOR(j, 2, min(k, len[i])) {
Add(g[i][k], c[j - 2][k - 2] * clen[i][j] % MOD);
}
}
}
//
FOR(i, 0, sz) total[0][i] = 1;
FOR(i, 1, n) {
FOR(j, 1, sz) {
dp[i][j] = dp[i - 1][j];// Not choose i
// Choose i
if (a[i] <= exist[j - 1] && exist[j] <= b[i]) {
int cnt = 0;
FORD(k, i, 1) {
if (a[k] <= exist[j - 1] && exist[j] <= b[k]) {
cnt++;
if (cnt == 1) {
Add(dp[i][j], total[k - 1][j - 1] * 1ll * len[j] % MOD);
}
else Add(dp[i][j], total[k - 1][j - 1] * g[j][cnt] % MOD);
}
}
}
}
total[i][0] = 1;
FOR(j, 1, sz) total[i][j] = (dp[i][j] + total[i][j - 1]) % MOD;
}
cout << (total[n][sz] - 1 + MOD) % MOD;
}
