#include "bits/stdc++.h"
using namespace std;
#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif
const int maxn = 505;
const int mod = 1e9 + 7;
int n, a[maxn], b[maxn];
int inv[maxn];
vector<int> cmp;
int f[maxn];
int add(int x, int y) {
if (y < 0) y += mod;
x += y;
if (x >= mod) x -= mod;
return x;
}
int power(int a, int b) {
int res = 1;
while (b) {
if (b & 1) res = 1ll * res * a % mod;
a = 1ll * a * a % mod;
b >>= 1;
}
return res;
}
void solve() {
cin >> n;
for (int i = 1; i <= n; ++i) {
cin >> a[i] >> b[i];
cmp.push_back(a[i]);
cmp.push_back(b[i] + 1);
}
cmp.push_back(0);
sort(cmp.begin(), cmp.end());
cmp.erase(unique(cmp.begin(), cmp.end()), cmp.end());
int sz = (int)cmp.size() - 1;
f[0] = 1;
for (int i = 1; i < sz; ++i) {
int l = cmp[i + 1] - cmp[i];
for (int j = n; j; --j) {
if (cmp[i] >= a[j] and cmp[i] <= b[j]) {
int nf = 0;
int cnk = 1;
int cnt = 0;
for (int k = j; k; --k) {
if (cmp[i] >= a[k] and cmp[i] <= b[k]) {
cnk = 1ll * cnk * inv[cnt + 1] % mod * (l + cnt) % mod;
++cnt;
}
nf = add(nf, 1ll * f[k - 1] * cnk % mod);
}
f[j] = add(f[j], nf);
}
}
}
int res = 0;
for (int i = 1; i <= n; ++i) res = add(res, f[i]);
cout << res;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
inv[0] = 1;
for (int i = 1; i < maxn; ++i) inv[i] = power(i, mod - 2);
solve();
return 0;
}
