#include <bits/stdc++.h>
#define ll long long
using namespace std;
const ll mod = (ll) 1e9+7;
int n, a[505], b[505];
ll f[505][3005];
ll g[505];
ll fact[505], inv[505];
ll Ckn(int x,int y){
return fact[y] * inv[x] % mod * inv[y-x] % mod;
}
ll mod_inverse(ll a){
ll r1 = a, r2 = mod, x1 = 1,x2 = 0, q, tmp;
while(r2 != 0){
q = r1 / r2;
tmp = x1 - q * x2;
x1 = x2;
x2 = tmp;
tmp = r1 % r2;
r1 = r2;
r2 = tmp;
}
return (x1+mod)%mod;
}
int main(){
fact[0] = 1;
for(int i=1;i<=500;i++)
fact[i] = fact[i-1] * i % mod;
for(int i=0;i<=500;i++)
inv[i] = mod_inverse(fact[i]);
//freopen("2_11.in","r",stdin);
iostream::sync_with_stdio(0);
cin >> n;
vector <int> lst;
for(int i=1;i<=n;i++)
cin >> a[i] >> b[i],
lst.push_back(a[i]),
lst.push_back(b[i]);
sort(lst.begin(), lst.end());
lst.resize(unique(lst.begin(),lst.end()) - lst.begin());
vector <pair<int,int> > range;
for(int i=0;i<lst.size();i++){
range.push_back({lst[i], lst[i]});
if (i != lst.size() - 1 && lst[i]+1 <= lst[i+1]-1)
range.push_back({lst[i]+1, lst[i+1]-1});
}
//range.clear(); for(int i=1;i<=n;i++) range.push_back({i,i});
range.insert(range.begin(), {-1,-1});
g[0] = 1;
ll ans = 0;
for(int j = 1;j < range.size();j ++){
// f[i][j] = cnt of way that end at i and value of i in range j
int len = range[j].second - range[j].first + 1;
ll arr[505], sumG[505];
arr[0] = 1;
sumG[0] = g[0];
for(int i=1;i<=n;i++)
sumG[i] = (sumG[i-1] + g[i]) % mod,
arr[i] = arr[i-1] * (len+1-i) % mod;
for(int i=1;i<=n;i++){
if (!(a[i] <= range[j].first && range[j].second <= b[i])) continue;
int possiBoat = 0;
ll tmp = 0;
for(int ii=i;ii>=1;ii--){
if (!(a[ii] <= range[j].first && range[j].second <= b[ii])) continue;
possiBoat++;
if (possiBoat == 1){
f[i][j] = (f[i][j] + sumG[ii-1] * arr[possiBoat] % mod) % mod;
}
else{
for(int k=2;k<=min(len, possiBoat);k++){
f[i][j] = (f[i][j] + sumG[ii-1] * Ckn(k-2, possiBoat-2) % mod * arr[k] % mod * inv[k] % mod) % mod;
}
}
}
ans = (ans + f[i][j]) % mod;
}
for(int i=0;i<=n;i++){
g[i] = (g[i] + f[i][j]) % mod;
}
}
// for(int j=1;j<range.size();j++){
// for(int i=1;i<=n;i++)
// cout << f[i][j] << ' ';
// cout << endl;
// }
cout << ans;
}
