#include <iostream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <cstring>
#include <chrono>
#include <vector>
#include <map>
#include <random>
#include <set>
#include <algorithm>
#include <math.h>
#include <cstdio>
#include <stdio.h>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <deque>
#include <cassert>
#include <stack>
#include <bits/stdc++.h>
using namespace std;
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
// typedef tree <int, null_type, less <int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
#define mp make_pair
#define f first
#define se second
#define pb push_back
#define ppb pop_back
#define emb emplace_back
#define ll long long
#define ull unsigned long long
#define cntbit(x) __builtin_popcount(x)
#define endl '\n'
#define uset unordered_set
#define umap unordered_map
#define pii pair<int, int>
#define ld long double
#define pll pair<long long, long long>
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T> inline T range(T l, T r) {
return uniform_int_distribution<T>(l, r)(rng);
}
template <typename T> void Min(T &a, T b) {
a = min(a, b);
}
template <typename T> void Max(T &a, T b) {
a = max(a, b);
}
const int mod = 1e9 + 7;
const int inf = 0x3f3f3f3f;
const int N = 5e2 + 15;
int n;
pii a[N];
int dp[N][N];
inline int add(int a, int b) {
a += b;
if(a >= mod)
return a - mod;
if(a < 0)
return a + mod;
return a;
}
inline void add_t(int &a, int b) {
a = add(a, b);
}
inline int mul(int a, int b) {
return 1LL * a * b % mod;
}
inline void mul_t(int &a, int b) {
a = mul(a, b);
}
main() {
ios_base::sync_with_stdio(0); cout.tie(0); cin.tie(0);
// freopen("input.txt", "r", stdin);
cin >> n;
for(int i = 1; i <= n; ++i)
cin >> a[i].f >> a[i].se;
for(int i = 1; i <= n; ++i) {
for(int j = 1; j < i; ++j) {
for(int prob = 0; prob <= n; ++prob) {
if(a[i].se > a[j].se) {
int st = max(a[j].se + 1, a[i].f);
for(; st <= a[i].se; ++st) {
int new_prob = (st - a[j].se - 1) + prob; // (st - a[j].se - 1) ?
if(new_prob > n) {
add_t(dp[i][n], mul(a[i].se - st + 1, dp[j][prob]));
break;
}
add_t(dp[i][new_prob], dp[j][prob]);
}
}
for(int k = min(a[j].se, a[i].se); k >= a[i].f; --k) {
int new_prob = prob - (a[j].se - k + 1);
if(new_prob < 0)
break;
add_t(dp[i][new_prob], dp[j][prob]);
}
}
}
for(int j = 0; a[i].f + j <= a[i].se; ++j) {
if(j >= n) {
add_t(dp[i][n], a[i].se - (a[i].f + j) + 1);
break;
}
add_t(dp[i][j], 1);
}
}
int ans = 0;
for(int i = 1; i <= n; ++i)
for(int j = 0; j <= n; ++j)
add_t(ans, dp[i][j]);
cout << ans << endl;
return 0;
}
