#include <bits/stdc++.h>
// #pragma GCC optimize ("Ofast,unroll-loops")
// #pragma GCC target ("avx2")
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pp;
#define per(i,r,l) for(int i = (r); i >= (l); i--)
#define rep(i,l,r) for(int i = (l); i < (r); i++)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define pb push_back
#define ss second
#define ff first
void err(istringstream *iss){}template<typename T,typename ...Args> void err(istringstream *iss,const T &_val, const Args&...args){string _name;*iss>>_name;if(_name.back()==',')_name.pop_back();cerr<<_name<<" = "<<_val<<", ",err(iss,args...);}
void IOS(){
cin.tie(0) -> sync_with_stdio(0);
// #ifndef ONLINE_JUDGE
// #define er(args ...) cerr << __LINE__ << ": ", err(new istringstream(string(#args)), args), cerr << endl
// freopen("inp.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
// #else
// #define er(args ...) 0
// #endif
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const ll mod = 1e9 + 7, maxn = 5e2 + 5, lg = 17, inf = ll(1e18) + 5, p = 9973;
ll pw(ll a,ll b,ll md=mod){if(!b)return 1;ll k=pw(a,b>>1ll,md);return k*k%md*(b&1ll?a:1)%md;}
ll dp[maxn][maxn<<1], a[maxn], b[maxn];
ll inv[maxn];
int main(){ IOS();
inv[0] = 1;
rep(i,1,maxn) inv[i] = pw(i, mod-2);
int n; cin >> n;
vector<int> p{0};
rep(i,1,n+1){
cin >> a[i] >> b[i];
b[i]++;
p.pb(a[i]), p.pb(b[i]);
}
sort(all(p)), p.erase(unique(all(p)), end(p));
int m = sz(p);
rep(i,0,m) dp[0][i] = 1;
rep(i,1,n+1){
int t = upper_bound(all(p), a[i]) - begin(p);
rep(j,t,m){
dp[i][j] = dp[i][j-1];
if(p[j] > b[i]) continue;
ll cr = p[j] - p[j-1];
int s = 1;
per(k,i-1,0){
dp[i][j] += cr*dp[k][j-1]%mod;
dp[i][j] %= mod;
if(a[k] <= p[j-1] && b[k] >= p[j]){
cr = cr*(s + p[j] - p[j-1])%mod;
s++;
cr = cr*inv[s]%mod;
}
}
// er(i, j, p[j], dp[i][j]);
}
}
ll ans = 0;
rep(i,1,n+1) ans += dp[i][m-1], ans %= mod;
cout << ans << '\n';
return 0;
}
