//```// YF YUSUF #include <bits/stdc++.h> using namespace std; #ifdef YF_CHECK bool LOCAL = 1; #else #pragma GCC target("avx2") #pragma GCC optimize ("unroll-loops") #pragma GCC optimize ("inline") #pragma GCC optimize ("Ofast") #pragma GCC optimize ("O3") bool LOCAL = 0; #endif using i128 = __int128; using ll = long long; using ld = long double; 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>bool MIN(T&a,T b){bool ret=(a>b);if(ret)a=b;return ret;} template<class T>bool MAX(T&a,T b){bool ret=(a<b);if(ret)a=b;return ret;} #define rall(a) a.rbegin(),a.rend() #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 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;} ll lg(ll x){return (x ? 63 - __builtin_clzll(x) : -1);} const ll mod=998244353; const ll INF=1e18; const ll inf=1e9+7; const ll N =5e2+7; ll n, a[N], b[N]; class treap{ struct node{ ll key, priority; ll sum, val, size, add; node *l = nullptr, *r=nullptr; node(ll key,ll value):key(key), val(value), priority(MT()){ sum = value; size = 1; add = 0; } } *root = nullptr; static ll key (node *n){return n ? n->key : 0;} static ll sum (node *n){return n ? n->sum : 0;} static ll val (node *n){return n ? n->val : 0;} static ll add (node *n){return n ? n->add : 0;} static ll size(node *n){return n ? n->size : 0;} static void update(node *n){ if(n){ n->size = 1 + size(n->l) + size(n->r); n->sum = (n->val + sum(n->l) + sum(n->r)) % inf; } } static void push(node *n){ if(n){ if(n->l) n->l->add = (n->add + n->l->add); if(n->r) n->r->add = (n->add + n->r->add); n->val = (n->val + n->add) % inf; n->sum = (n->sum + n->add * n->size) % inf; n->add = 0; } } static node *merge(node *a, node *b){ if(!a || !b) return a ? a : b; push(a); push(b); if(a->priority > b->priority){ a->r = merge(a->r, b); update(a); return a; } else { b->l = merge(a, b->l); update(b); return b; } } static void split(node *n, int key, node* &a, node* &b){ if(!n){ a = b = nullptr; return; } push(n); if(n->key < key){ split(n->r, key, n->r, b); a = n; } else { split(n->l, key, a, n->l); b = n; } update(a); update(b); } public: void insert(int key){ node *less, *equal, *greater; split(root, key, less, greater); split(greater, key + 1, equal, greater); if(!equal) equal = new node(key, 0); // cout<<key<<" "<<size(equal)<<" size of eq\n"; root = merge(less, merge(equal, greater)); } void add(ll l, ll r,ll x){ node *less, *equal, *greater; split(root, l, less, greater); split(greater, r + 1, equal, greater); // cout<<l<<" "<<r<<" "<<size(less)<<" "<<size(equal)<<" "<<size(greater)<<"\n"; if(equal) equal->add = (equal->add + x) % inf; // else // cout<<"wasted\n"; root = merge(less, merge(equal, greater)); } ll get(ll l,ll r){ node *less, *equal, *greater; split(root, l, less, greater); split(greater, r + 1, equal, greater); ll res = sum(equal); root = merge(less, merge(equal, greater)); return res; } }; void YF_MAIN(ll TEST){ cin>>n; treap tr; tr.insert(0); tr.add(0, 0, 1); for(int i=1;i<=n;i++){ cin>>a[i]>>b[i]; for(int x = b[i]; x>=a[i]; x--){ ll sum = tr.get(0, x-1); // cout<<i<<" "<<sum<<" "<<x<<"\n"; tr.insert(x); tr.add(x, x, sum); } } cout<<(tr.get(0, inf) + inf - 1) % inf; } const bool TECT=0; const bool FLSH=1; const ll SN=1e0 + 7; ll SM[SN]; const ll FN=1e0 + 7; ll FACT[FN], inv[FN], FMOD=inf; ll PNK(ll n,ll k){return FACT[n] *inv[n-k]%FMOD;} ll CNK(ll n,ll k){return PNK(n,k)*inv[k ]%FMOD;} 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(FACT[i],FMOD-2,FMOD); } } signed main(){ // freopen(("input.txt"),"r",stdin);freopen(("output.txt"),"w",stdout); if(FLSH){ ios_base::sync_with_stdio(0); cout.setf(ios::fixed); cout.precision(0); cout.tie(0); cin.tie(0); } 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; } // YF YUSUF ```