#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#include "bits/stdc++.h"
using namespace std;
#define for_(i, s, e) for (int i = s; i < (int) e; i++)
#define for__(i, s, e) for (ll i = s; i < e; i++)
typedef long long ll;
typedef vector<int> vi;
typedef array<int, 2> ii;
// #define endl '\n'
namespace speedy_io {
int read_nonneg() {
int c;
while ((c = getchar_unlocked()) < '0' || c > '9');
int v = c - '0';
while ((c = getchar_unlocked()) >= '0' && c <= '9') {
v = (v << 3) + (v << 1) + (c - '0');
}
return v;
}
const int max_ll_size = 20;
void put_nonneg(ll n) {
int i = max_ll_size;
char output_buffer[max_ll_size];
do {
output_buffer[--i] = (n % 10) + '0';
n /= 10;
} while (n);
do {
putchar_unlocked(output_buffer[i]);
} while (++i < max_ll_size);
}
}
using namespace speedy_io;
const ll mod = 1e9+7;
ll power(ll x, ll y) {
if (y == 0) return 1;
ll p = power(x, y/2) % mod;
p = (p * p) % mod;
return (y%2 == 0)? p : (x * p) % mod;
}
ll modInverse(ll a) {
return power(a, mod-2);
}
const int MXN = 500;
ll choose[4*MXN+2][MXN+1], dp[2][MXN+1][MXN+1][2];
int main() {
#ifdef mlocal
freopen("test.in", "r", stdin);
#endif
// ios_base::sync_with_stdio(false);
// cin.tie(0);
int n = read_nonneg();
vector<ii> lt(n);
vi raw(2*n);
for_(i, 0, n) {
lt[i][0] = read_nonneg(), lt[i][1] = read_nonneg();
lt[i][1]++;
raw[2*i] = lt[i][0], raw[2*i+1] = lt[i][1];
}
sort(raw.begin(), raw.end());
raw.resize(unique(raw.begin(), raw.end()) - raw.begin());
vector<ii> seg;
// int pre = -1;
for_(i, 1, raw.size()) {
// if (pre < raw[i] and pre != -1) seg.push_back({pre, raw[i]-1});
seg.push_back({raw[i-1], raw[i]-1});
// pre = raw[i]+1;
}
int ns = seg.size();
// cout << ns << endl;
// for (auto i: seg) cout << i[0] << " " << i[1] << endl;
memset(choose, 0, sizeof(choose)); memset(dp, 0, sizeof(dp));
vector<ll> modInv(n+1);
for_(i, 1, n+1) modInv[i] = modInverse(i);
for_(i, 0, ns) {
choose[i][0] = 1;
for_(r, 1, min(n, seg[i][1]-seg[i][0]+1) + 1) choose[i][r] = (((choose[i][r-1] * (seg[i][1]-seg[i][0]-r+2)) % mod) * modInv[r]) % mod;
}
bool valid[n];
int c = 0;
for (int s = ns-1; s >= 0; s--) {
memset(dp[c], 0, sizeof(dp[c]));
for_(idx, 0, n) valid[idx] = seg[s][0] >= lt[idx][0] and seg[s][1] < lt[idx][1];
for (int ct = min(n-1, seg[s][1]-seg[s][0]+1); ct >= 0; ct--) {
dp[c][ct][n][0] = choose[s][ct];
for (int idx = n-1; idx >= 0; idx--) {
if (valid[idx]) dp[c][ct][idx][1] += dp[c][ct+1][idx+1][0];
if (dp[c][ct][idx][1] >= mod) dp[c][ct][idx][1] -= mod;
dp[c][ct][idx][1] += (choose[s][ct] * (s < ns-1 ? dp[1-c][0][idx][1] : 0)) % mod;
if (dp[c][ct][idx][1] >= mod) dp[c][ct][idx][1] -= mod;
dp[c][ct][idx][0] = dp[c][ct][idx][1] + dp[c][ct][idx+1][0];
if (dp[c][ct][idx][0] >= mod) dp[c][ct][idx][0] -= mod;
}
}
c = 1-c;
}
put_nonneg((dp[1-c][0][0][0]-1+mod) % mod);
printf("\n");
}
