#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i = a; i<int(b);++i)
#define all(v) v.begin(),v.end()
#define sz(v) v.size()
#define trav(a,c) for(auto a: c)
typedef long long ll;
typedef vector<ll> vi;
typedef pair<ll,ll> pii;
ll mod = 1e9+7;
class Node {
public:
ll val = 0;
ll dn,up;
Node *left;
Node *right;
bool children = false;
Node(ll _dn, ll _up){
dn = _dn;
up = _up;
}
void ensure(){
if(dn+1==up) return;
if(!children){
children = true;
left = new Node(dn,(dn+up)/2);
right = new Node((dn+up)/2,up);
}
}
ll update(ll pos, ll v){
if(pos<dn||pos>=up) return val;
if(dn+1==up) return val = (val+v)%mod;
ensure();
ll l = left->update(pos,v);
ll r = right->update(pos,v);
return val = (l+r)%mod;
}
ll query(ll a, ll b){
if(b<=dn||a>=up) return 0;
if(a<=dn&&b>=up) return val;
ensure();
return (left->query(a,b)+right->query(a,b))%mod;
}
};
int main(){
cin.sync_with_stdio(false);
ll n;
cin>>n;
vi a,b;
a.resize(n);
b.resize(n);
//posLastStart.resize(n);
//posLast.push_back(-1);
rep(i,0,n) {
cin>>a[i]>>b[i];
//posLastStart[i] = posLast.size();
//rep(j,a[i],b[i]+1) posLast.push_back(j);
}
//mem.resize(posLastStart.size()+1,vi(n+1,-1));
//cout<<(getNum(0,0)+mod-1)%mod<<endl;
Node dp(0,1e10);
dp.update(0,1);
ll ans = 0;
rep(i,0,n){
vi u(b[i]+1-a[i]);
rep(j,a[i],b[i]+1) {
ans = (ans + (u[j-a[i]] = dp.query(0,j)))%mod;
}
rep(j,a[i],b[i]+1) {
dp.update(j,u[j-a[i]]);
}
}
cout<<ans<<endl;
_Exit(0);
}
