#include <bits/stdc++.h>
using namespace std;
typedef long long Long;
typedef pair <int, int> pii;
const int mod = 1000000007;
Long bigmod(int x, int y) {
if(y == 0) return 1;
if(y & 1) return (bigmod(x, y-1) * x) % mod;
Long m = bigmod(x, y >> 1);
return (m * m) % mod;
}
Long inv[505];
int a[505];
int b[505];
int n;
int cntG;
vector <int> g[1005];
int cost[1005];
int c[505][505];
bool overlap(int l, int r, int i) {
if(a[i] <= l and r <= b[i]) return true;
else return false;
}
bool veryBad(int l, int r, int i) {
if(l <= a[i] and a[i] <= r) return true;
if(l <= b[i] and b[i] <= r) return true;
else return false;
}
void divideGroups() {
vector <pii> v;
for(int i = 1; i <= n; i++) {
v.push_back(pii(a[i], 0));
v.push_back(pii(b[i], 1));
}
sort(v.begin(), v.end());
int prev = v.at(0).first;
int now;
for(int i = 1; i < (int) v.size(); i++) {
pii x = v.at(i);
if(x.second == 0) {
now = x.first - 1;
} else {
now = x.first;
}
cost[i] = now - prev + 1;
for(int j = 1; j <= n; j++) {
if(prev > now) continue;
if(overlap(prev, now, j)) {
g[i].push_back(j);
} else {
assert(veryBad(prev, now, j) == false);
}
}
prev = now + 1;
}
cntG = v.size() - 1;
}
int calc(int costx, int x) {
Long sum = 0;
Long nCr = 1;
for(int i = 1; i <= x; i++) {
if(i > costx) break;
nCr *= (costx - i + 1);
nCr %= mod;
nCr *= inv[i];
nCr %= mod;
sum += c[x - 1][i - 1] * nCr;
sum %= mod;
}
return sum;
}
int fn[1005][505];
int gn[1005][505];
int dp(int group, int x) {
if(group > cntG) return 1;
if(fn[group][x] != -1) return fn[group][x];
Long ans = dp(group + 1, x);
int k = 0;
for(int i : g[group]) {
if(i < x) continue;
++k;
ans += 1LL * gn[group][k] * dp(group + 1, i + 1);
ans %= mod;
}
return fn[group][x] = ans;
}
int main(int argc, char const *argv[])
{
ios_base :: sync_with_stdio (false);
cin.tie (0);
for(int i = 1; i <= 500; i++) {
inv[i] = bigmod(i, mod - 2);
}
for(int i = 0; i <= 500; i++) c[i][0] = 1;
for(int i = 1; i <= 500; i++) {
for(int j = 1; j <= 500; j++) {
c[i][j] = c[i - 1][j] + c[i - 1][j - 1];
c[i][j] %= mod;
}
}
cin >> n;
for(int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
}
divideGroups();
for(int i = 1; i <= cntG; i++) {
int size = g[i].size();
for(int j = 1; j <= size; j++) {
gn[i][j] = calc(cost[i], j);
}
}
memset(fn, -1, sizeof fn);
int ans = dp(1, 1);
ans -= 1;
if(ans < 0) ans += mod;
cout << ans << endl;
return 0;
}
