#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define SIZE(a) ((int)(a).size())
#define ALL(a) (a).begin(), (a).end()
using ll = long long;
using K = long double;
const int inf = 1000*1000*1000 + 7;
const int mod = 1000*1000*1000 + 7;
const int N = 1005;
int power(int a, int n) {
int result = 1;
while (n > 0) {
if (n % 2) {
result = (1LL*result*a) % mod;
}
a = (1LL*a*a) % mod;
n /= 2;
}
return result;
}
int inv(int a) {
return power(a, mod-2);
}
void add(int &x, int y) {
x += y;
if (x >= mod) x -= mod;
}
int n, m, l[N], r[N];
vector<int> d;
int f[N][N], g[N][N];
int inside(int id, int piece) {
return l[id] <= d[piece] && r[id] >= d[piece+1];
}
int iv[N];
int c[N][N];
int cur[N];
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n;
REP(i, n) {
cin >> l[i] >> r[i];
++r[i];
d.push_back(l[i]);
d.push_back(r[i]);
}
sort(d.begin(), d.end());
d.erase(unique(d.begin(), d.end()), d.end());
m = SIZE(d)-1;
f[0][0] = 1;
for (int i = 1; i <= n; ++i) {
iv[i] = inv(i);
}
REP(i, N) {
c[i][0] = c[i][i] = 1;
for (int j = 1; j < i; ++j) {
add(c[i][j], c[i-1][j-1]);
add(c[i][j], c[i-1][j]);
}
}
REP(w, m) {
int len = d[w+1]-d[w];
int first = len;
for (int j = 0; j <= n; ++j) {
first = 1LL*first*(len-j-1)%mod*iv[j+2] % mod;
cur[j] = first;
}
for (int i = 0; i <= n; ++i) {
for (int j = 0; j <= i; ++j) {
add(g[i][w], 1LL*cur[j]*c[i][j] % mod);
}
}
}
REP(i, n) {
REP(j, m+1) add(f[i+1][j], f[i][j]);
REP(j, m) {
add(f[i][j+1], f[i][j]);
if (!inside(i, j)) continue;
add(f[i+1][j+1], 1LL*f[i][j]*(d[j+1]-d[j]) % mod);
int cnt = -1;
for (int nxt = i+1; nxt < n; ++nxt) {
if (!inside(nxt, j)) continue;
++cnt;
add(f[nxt+1][j+1], 1LL*f[i][j]*g[cnt][j] % mod);
}
}
}
int result = mod-1;
REP(i, m+1) add(result, f[n][i]);
cout << result << '\n';
}
