import java.util.Arrays;
import java.util.HashSet;
import java.util.Scanner;

class Main {
	public static void main(String[] args) {
		new Main().run();
	}

	final long MOD = 1_000_000_000 + 7;
	long[] karamatsu_prob = new long[200];
	long[] fac = new long[200];
	long[] ifac = new long[200];

	long pow(long a, long n) {
		long ret = 1;
		for (; n > 0; n >>= 1, a = a * a % MOD) {
			if (n % 2 == 1) {
				ret = ret * a % MOD;
			}
		}
		return ret;
	}

	long inv(long a) {
		return pow(a, MOD - 2);
	}

	{
		fac[0] = fac[1] = 1;
		ifac[0] = ifac[1] = 1;
		for (int i = 2; i < fac.length; ++i)
			fac[i] = fac[i - 1] * i % MOD;
		for (int i = 2; i < ifac.length; ++i) {
			ifac[i] = inv(fac[i]);
		}
	}

	long comb(int n, int k) {
		return fac[n] * ifac[k] % MOD * ifac[n - k] % MOD;
	}

	{
		karamatsu_prob[0] = 1;
		karamatsu_prob[1] = 1;
		for (int i = 2; i < karamatsu_prob.length; ++i) {
			for (int j = 0; j <= i - 1; j += 2) {
				karamatsu_prob[i] += karamatsu_prob[j] * karamatsu_prob[i - j - 1] % MOD * comb(i - 1, j) % MOD;
				karamatsu_prob[i] %= MOD;
			}
		}
		for (int i = 0; i < karamatsu_prob.length; ++i) {
			karamatsu_prob[i] = karamatsu_prob[i] * ifac[i] % MOD;
		}
	}

	void run() {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		++N;
		long[] l = new long[N];
		long[] r = new long[N];
		HashSet<Long> set = new HashSet<>();
		for (int i = 1; i < N; ++i) {
			l[i] = sc.nextLong();
			r[i] = sc.nextLong();
			set.add(l[i]);
			set.add(r[i]);
			// [l[i],r[i])
		}
		set.add((long) 1e9);
		set.add((long) 1e9 + 1);
		l[0] = (long) 1e9;
		r[0] = (long) 1e9 + 1;
		long[] a = new long[set.size()];
		int sz = 0;
		for (long v : set) {
			a[sz] = v;
			++sz;
		}
		Arrays.sort(a);
		// [a[i],a[i+1]]
		long[][] p = new long[N][sz];
		for (int i = 0; i < N; ++i) {
			for (int j = 0; j + 1 < sz; ++j) {
				if (!(l[i] <= a[j] && a[j + 1] <= r[i]))
					continue;
				p[i][j] = (a[j + 1] - a[j]) * inv(r[i] - l[i]) % MOD;
			}
		}
		long[][] prob = new long[N][sz];
		prob[0][sz - 2] = 1;
		for (int t = 0; t + 1 < N; ++t) {
			for (int src = 0; src + 1 < sz; ++src) {
				for (int dst = 0; dst + 1 < sz; ++dst) {
					if ((t % 2 == 1 && src >= dst) || (t % 2 == 0 && src <= dst))
						continue;
					long prob_cur = prob[t][src];
					for (int i = 1; t + i < N; ++i) {
						prob_cur = prob_cur * p[t + i][dst] % MOD;
						if (prob_cur == 0)
							break;
						prob[t + i][dst] += prob_cur * karamatsu_prob[i] % MOD;
						prob[t + i][dst] %= MOD;
					}
				}
			}
		}
		long ans = 0;
		for (int i = 0; i < prob[N - 1].length; ++i)
			ans = (ans + prob[N - 1][i]) % MOD;
		System.out.println(ans);

	}

	void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}
}