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import java.io.*;
import java.util.*;
class Main {
static final int MOD = 1000000007;
static long add(long a, long b) {
a += b;
if (a >= MOD) a -= MOD;
return a;
}
static long mul(long a, long b) {
return (a * b) % MOD;
}
public static void main(String[] args) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
PrintWriter out = new PrintWriter(System.out);
int n = Integer.parseInt(br.readLine());
int[] l = new int[n];
int[] r = new int[n];
TreeSet<Integer> set = new TreeSet<>();
for (int i = 0; i < n; i++) {
String[] s = br.readLine().split(" ");
l[i] = Integer.parseInt(s[0]);
r[i] = Integer.parseInt(s[1]);
set.add(l[i]);
set.add(r[i] + 1);
}
int m = set.size();
int[] vals = new int[m];
int idx = 0;
for (int v : set) vals[idx++] = v;
long[] dp = new long[n + 1];
dp[0] = 1;
for (int i = 0; i < m - 1; i++) {
int L = vals[i];
int R = vals[i + 1] - 1;
int len = R - L + 1;
int cnt = 0;
for (int j = 0; j < n; j++) {
if (l[j] <= L && r[j] >= R) cnt++;
}
if (cnt == 0) continue;
long[] ndp = new long[n + 1];
for (int used = 0; used <= n; used++) {
if (dp[used] == 0) continue;
long ways = 1;
for (int take = 0; take <= cnt && used + take <= n; take++) {
if (take > len) break;
if (take > 0) {
ways = mul(ways, (len - take + 1));
ways = mul(ways, inv(take));
}
ndp[used + take] = add(ndp[used + take], mul(dp[used], ways));
}
}
dp = ndp;
}
long ans = 0;
for (int i = 1; i <= n; i++) ans = add(ans, dp[i]);
out.println(ans);
out.flush();
}
static long inv(long x) {
return pow(x, MOD - 2);
}
static long pow(long a, long b) {
long r = 1;
while (b > 0) {
if ((b & 1) == 1) r = (r * a) % MOD;
a = (a * a) % MOD;
b >>= 1;
}
return r;
}
}
