#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[N][2 * N], su[N][2 * 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;
dp[0][0] = 1;
fill_n(su[0], w, 1);
for (int b = 1; b <= n; ++b) {
copy_n(dp[b - 1], w, dp[b]);
for (int i = w - 1; i > 0; --i) {
ll cn = val[i] - val[i - 1];
ll cj = cn;
for (int j = 1, o = b; j <= b && p[o][0] <= val[i - 1] && val[i] <= p[o][1]; ++j, --o) {
//dp[b][i] += c(val[i] - val[i - 1], j) * su[o - 1][i - 1]
(dp[b][i] += cj * su[o - 1][i - 1]) %= MOD;
cj = cj * (cn - j) % MOD * inv[j + 1] % MOD;
}
}
su[b][0] = dp[b][0];
for (int i = 1; i < w; ++i)
su[b][i] = (dp[b][i] + su[b][i - 1]) % MOD;
}
cout << (su[n][w - 1] + MOD - 1) % MOD << endl;
}
