#include <bits/stdc++.h>
using namespace std;
#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 llint long long
#define sz(x) (x.size())
#define LL(x) (x * 2)
#define RR(x) (x * 2 + 1)
#define fi first
#define se second
#define db(x) cout << #x << " = " << x << endl;
#define BIT(x, i) ((x >> i) & 1)
#define MASK(i) (1ll << i)
#define times clock() * 1.0 / CLOCKS_PER_SEC
void openFile() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
#ifdef Tr___
freopen("test.inp", "r", stdin);
freopen("test.out", "w", stdout);
#endif
}
const int maxN = 1e3 + 5;
const int maxM = 1e6 + 5;
const llint INF = 1e9 + 7;
int N;
vector<int> all;
int a[maxN], b[maxN];
llint dp[maxN][maxN], len[maxN], inv[maxN];
void enter() {
cin >> N;
FOR(i, 1, N) {
cin >> a[i] >> b[i];
all.push_back(a[i]);
all.push_back(b[i] + 1);
}
}
inline void add(llint &x, llint y) {
x = (x + y) % INF;
}
void solve() {
inv[1] = 1;
FOR(i, 2, maxN - 1) {
inv[i] = inv[INF % i] * (INF - INF / i) % INF;
}
sort(all.begin(), all.end());
all.erase(unique(all.begin(), all.end()), all.end());
FOR(i, 1, N) {
a[i] = upper_bound(all.begin(), all.end(), a[i]) - all.begin();
b[i] = upper_bound(all.begin(), all.end(), b[i]) - all.begin();
}
FOR(i, 1, all.size() - 1) {
len[i] = all[i] - all[i - 1];
}
FOR(i, 0, all.size() - 1) {
dp[0][i] = 1;
}
llint res = 0;
FOR(i, 1, N) {
FOR(j, a[i], b[i]) {
add(dp[i][j], dp[i - 1][j - 1] * len[j]);
llint num = 1, choose = len[j] - 1;
FORD(k, i - 1, 1) if (a[k] <= j && j <= b[k]) {
++num;
choose = choose * (len[j] + num - 2) % INF * inv[num] % INF;
if (choose == 0) break;
add(dp[i][j], dp[k - 1][j - 1] * choose % INF);
}
}
dp[i][0] = 1;
FOR(j, 1, all.size() - 1) {
add(dp[i][j], dp[i - 1][j] + dp[i][j - 1] - dp[i - 1][j - 1]);
add(dp[i][j], INF);
}
}
cout << (dp[N][all.size() - 1] - 1 + INF) % INF << endl;
}
int main() {
openFile();
enter();
solve();
return 0;
}
