/**
Problem: Boat
Source: APIO 2016 problem 1
*/
#include <iostream>
#include <algorithm>
#define long long long
using namespace std;
const int N = 500 + 2;
const int MOD = 1e9 + 7;
int Mul(int a, int b) { return (long) a * b % MOD; }
void Add(int &a, int b) { a += b; if (a >= MOD) a -= MOD; }
int Sum(int a, int b) { Add(a, b); return a; }
void Sub(int &a, int b) { a -= b; if (a < 0) a += MOD; }
int Pow(int x, int n)
{
if (n == 1) return x;
int t = Pow(x, n / 2); t = Mul(t, t);
return n & 1 ? Mul(t, x) : t;
}
int n, a[N], b[N];
int m, p[N * 2]; // left and right ends of ranges
int c[N][N]; // c[i][j] = choose j from i
int g[N * 2][N];
int ft[N], inv[N];
int f[N][N * 2];
void Prep() // precalculate all g(i, j)
{
ft[0] = 1; // calculate factorials and inverses
for (int i = 1; i <= n; ++i) ft[i] = Mul(ft[i - 1], i);
inv[n] = Pow(ft[n], MOD - 2);
for (int i = n - 1; i >= 0; --i)
inv[i] = Mul(inv[i + 1], i + 1);
c[0][0] = 1;
for (int i = 1; i <= n; ++i) // calculate all c(i, j) with i, j <= n
{
c[i][0] = 1;
for (int j = 1; j <= i; ++j)
c[i][j] = Sum(c[i - 1][j], c[i - 1][j - 1]);
}
for (int i = 1; i < m; ++i)
{
int tmp[N] = {}, len = p[i] - p[i - 1]; // tmp[i] = c(len, i)
tmp[0] = 1;
for (int j = 1; j <= min(n, len); ++j)
tmp[j] = Mul(Mul(tmp[j - 1], len - j + 1), inv[j]);
for (int j = 1; j <= n; ++j) // j schools can send, including the current one
for (int k = 1; k <= min(j, len); ++k) // k schools actually sent, including the current one
Add(g[i][j], Mul(c[j - 1][k - 1], tmp[k]));
}
}
void Solve()
{
int res = 0;
fill(f[0], f[0] + m, 1);
for (int i = 1; i <= n; ++i)
for (int j = 1; j < m; ++j)
{
if (a[i] <= p[j - 1] + 1 && p[j] <= b[i])
{
int cnt = 0; // number of schools that contain range j
for (int k = i; k >= 1; --k)
{
cnt += (a[k] <= p[j - 1] + 1 && p[j] <= b[k]);
Add(f[i][j], Mul(f[k - 1][j - 1], g[j][cnt]));
}
// cout << "f[" << i << "][" << j << "] = " << f[i][j] << '\n';
Add(res, f[i][j]);
}
Add(f[i][j], f[i][j - 1]);
}
cout << res;
}
int main()
{
cin >> n;
for (int i = 1; i <= n; ++i)
{
cin >> a[i] >> b[i];
p[m++] = a[i] - 1;
p[m++] = b[i];
}
sort(p, p + m);
m = unique(p, p + m) - p;
Prep();
Solve();
return 0;
}
