//```// YF YUSUF
#define YF ios_base::sync_with_stdio(0);cout.setf(ios::fixed);
#define YUSUF cout.precision(0);cout.tie(0);cin.tie(0);
// #include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <algorithm>
#include <cmath>
#include <numeric>
#include <queue>
#include <stack>
#include <cassert>
#include <climits>
#include <string>
#include <cstdlib>
#include <random>
#include <ctime>
using namespace std;
#ifdef YF_CHECK
bool Output=1;
#else
#pragma GCC optimize ("unroll-loops")
#pragma GCC optimize ("inline")
#pragma GCC optimize ("Ofast")
#pragma GCC optimize ("O3")
bool Output=0;
#endif
using ll = long long;
using ld = long double;
using sll = set <ll>;
using vll = vector <ll>;
using mll = map <ll,ll>;
using pll = pair <ll,ll>;
using vvl = vector <vll>;
using vpll = vector <pll>;
template<class T>T MIN(T&a,T b){a=min(a,b);return a;}
template<class T>T MAX(T&a,T b){a=max(a,b);return a;}
#define all(a) a.begin(),a.end()
#define sgr v+v+1,(tl+tr)/2+1,tr
#define sgl v+v,tl,(tl+tr)/2
#define pb push_back
#define ins insert
#define S second
#define F first
mt19937_64 MT(time(0));
ll BP(ll a,ll b,ll mod=1e9+7){
if(b==0)return 1;
ll q=BP(a,b/2,mod);
return ((q*q)%mod*(b%2?a:1ll))%mod;
}
ll f(ll x){return x*(x+1)/2;}
ll dup(ll a,ll b){return (a+b-1)/b;}
ll lcm(ll a,ll b){return a/__gcd(a,b)*b;}
ll invf(ll x){return (-1+sqrt(1+8*x))/2;}
const ll mod=998244353;
const ll INF=1e18;
const ll inf=1e9+7;
const ll N =1e6+7;
// ll t[4*N];
// ll merge(ll a,ll b){
// return (a+b)%inf;
// }
// void up(ll pos,ll x,ll v=1,ll tl=1,ll tr=n){
// if(tl==tr){
// t[v]+=x;
// t[v]%=inf;
// }
// else{
// ll tm=(tl+tr)/2;
// if(pos<=tm)up(pos,x,sgl);
// else up(pos,x,sgr);
// t[v]=merge(t[v+v],t[v+v+1]);
// }
// }
// ll get(ll l,ll r,ll v=1,ll tl=1,ll tr=n){
// if(l > tr || tl > r)return 0;
// if(l<= tl && tr<=r)return t[v];
// ll tm=(tl+tr)/2;
// return merge(get(l,r,sgl),get(l,r,sgr));
// }
const ll FN=1e6 + 7; ll FACT[FN], inv[FN], FMOD=inf;
ll PER(ll n,ll k){return FACT[n] *inv[n-k]%FMOD;}
ll CNK(ll n,ll k){return PER(n,k)*inv[k ]%FMOD;}
ll slow_cnk(ll n,ll k){
ll ans = 1;
MIN(k, n-k);
for(int i=1;i<=k;i++){
ans = (ans * (n-k+i))%FMOD;
ans = (ans * inv[i])%FMOD;
}
return ans;
}
ll get(ll l1,ll r1,ll l2,ll r2){
MAX(l2, l1);
MIN(r1, r2);
if(l2 > r1 || l1 > r2 || l1 > r1 || l2 > r2 )return 0;
// cout<<l1<<" "<<r1<<", "<<l2<<" "<<r2<<"\n";
ll n = max(r1, r2) - max(l1, l2) + 1;
ll k = min(r1, r2) - max(l1, l2);
return slow_cnk(n, k);
}
void YF_MAIN(ll TEST){
ll n;
cin>>n;
ll a[n+1]{},b[n+1]{};
ll dp[n+1]{};
ll sum = 0;
for(int i=1;i<=n;i++){
cin>>a[i]>>b[i];
dp[i] = b[i] - a[i] + 1;
for(int j=i-1;j>=1;j--){
if(a[j] > b[i])continue;
dp[i] += (b[i]-a[i]+1)*dp[j]-get(a[j], b[j], a[i], b[i]);
dp[i] %= inf;
}
sum += dp[i];
sum %= inf;
// cout<<dp[i]<<" ";
}
// cout<<"\n";
cout<<(sum + inf) % inf;
}
bool TECT=0;
bool OUTP=1;
ll lg(ll x){return (x ? 63 - __builtin_clzll(x) : -1);}
const ll SN=2e0 + 7; ll SM[SN];
void BEFORE(){
for(ll i=2;i<SN;i++){
if(SM[i])continue;
for(ll j=i;j<SN;j+=i)
MAX(SM[j],i);
}
FACT[0]=inv[0]=1;
for(int i=1;i<FN;i++){
FACT[i]=FACT[i-1]*i%FMOD;
inv[i]=BP(i,FMOD-2,FMOD);
}
}
signed main(){
// freopen(("input.txt"),"r",stdin);freopen(("output.txt"),"w",stdout);
if(OUTP){YF YUSUF}
cout<<(0 && Output ? "\nYF_OUTPUT:\n\n" : "");
int TEST=1;
if(TECT)
cin>>TEST;
BEFORE();
for(int T=1;T<=TEST;T++){
// cout<<"Case "<<T<<": ";
YF_MAIN(T);
cout<<(T==TEST ? "" : "\n");
}
return 0;
}
//```
