#include<bits/stdc++.h>
using namespace std;
const int N = 505, MOD = 1e9 + 7;
typedef long long ll;
vector<int> val;
typedef array<int, 2> ar;
ar p[N];
ll dp[2 * N][N], inv[N];
int main()
{
int n;
cin >> n;
val = {-1};
for (int i = 1; i <= n; ++i) {
cin >> p[i][0] >> p[i][1];
++p[i][1];
val.push_back(p[i][0]);
val.push_back(p[i][1]);
}
sort(val.begin(), val.end());
val.resize(unique(val.begin(), val.end()) - val.begin());
int w = val.size();
inv[1] = 1;
for (int i = 2; i <= n; ++i)
inv[i] = (MOD - MOD / i) * inv[MOD % i] % MOD;
for (int i = 0; i < w; ++i)
dp[i][0] = 1;
for (int b = 1; b <= n; ++b) {
for (int i = w - 1; i > 0; --i)
if (p[b][0] <= val[i - 1] && val[i] <= p[b][1]) {
int cn = val[i] - val[i - 1];
for (int j = min(cn, b); j >= 1; --j)
(dp[i][j] += dp[i][j - 1] * (cn - j + 1) % MOD * inv[j]) %= MOD;
}
for (int i = 1; i <= w; ++i)
dp[i][0] = accumulate(dp[i - 1], dp[i - 1] + n + 1, 0ll) % MOD;
}
cout << (dp[w][0] + MOD - 1) % MOD << endl;
}
