#include <bits/stdc++.h>
using namespace std;
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii ;
typedef pair<ll, ll> pll ;
typedef vector<pii> vii ;
typedef vector<int> veci ;
typedef vector<pll> vll ;
typedef vector<ll> vecll;
// find_by_order order_of_key
//#pragma GCC optimize("O3,unroll-loops")
//#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define F first
#define S second
#define pb push_back
#define endl '\n'
#define Mp make_pair
#define all(x) x.begin(), x.end()
#define debug(x) cerr << #x << " = " << x << endl
#define set_dec(x) cout << fixed << setprecision(x);
#define fast_io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io freopen("in.txt" , "r" , stdin) ; freopen("out.txt" , "w" , stdout);
#define lb lower_bound
#define ub upper_bound
#define for1(n) for(int i=1;i<=n;i++)
#define for0(n) for(int i=0;i<n;i++)
#define forn(n) for(int i=n;i>0;i--)
#define pq priority_queue <int, vector<int>, greater<int>>
#define pq2 priority_queue <pair<int,pii>, vector<pair<int,pii>>, greater<pair<int,pii>>>
const ll mod = 1e9+7 ;// 998244353 ;// 1e9+9;
ll inf=1e18;
const int N=2e5+100,L=21,bs=701,NN=1e6;
int E[N],n,m,k,q,is[N];
vector<int>g[N];
bitset<N>iss;
pii A[N];
pq B[N],C[N];
set<pair<int,pii>> D;
ll ans;
pii merg(pii a,pii b,bool o){
//b->a
if(B[a.F].size()+C[a.F].size()<B[b.F].size()+C[b.F].size())swap(a,b);
if(a.S==0)D.erase({C[a.F].top(),{a.F,1}});
else D.erase({B[a.F].top(),{a.F,0}});
if(b.S==0)D.erase({C[b.F].top(),{b.F,1}});
else D.erase({B[b.F].top(),{b.F,0}});
if(o^a.S^b.S)
swap(B[b.F],C[b.F]);
while(B[b.F].size()){
B[a.F].push(B[b.F].top());
B[b.F].pop();
}
while(C[b.F].size()){
C[a.F].push(C[b.F].top());
C[b.F].pop();
}
if(a.S!=0)D.insert({B[a.F].top(),{a.F,0}});
else D.insert({C[a.F].top(),{a.F,1}});
return a;
}
int main(){
fast_io
cin>>n;
for1(n){
int x,y;cin>>x>>y;
is[x]=y;
}
for1(n*2){
if(is[i]==0){
pair<int,pii>p=(*D.begin());D.erase(D.begin());
int x=p.S.F,o=p.S.S;
if(o==0){
B[x].pop();
D.insert({B[x].top(),{x,0}});
}
else{
C[x].pop();
D.insert({C[x].top(),{x,1}});
}
continue;
}
vector<pair<int,pii>>vec;
while(D.size() && (*D.begin()).F<is[i]){
vec.pb((*D.begin()));
D.erase(D.begin());
}
B[i].push(is[i]);B[i].push(mod+i*3);
C[i].push(mod+i*3+1);
D.insert({mod+i*3+1,{i,1}});
pii cand={i,0};iss[i]=1;
for(pair<int,pii>p:vec){
if(iss[p.S.F])return cout<<"0\n",0;
iss[p.S.F]=1;
cand=merg(cand,p.S,(cand.F==i));
}
iss[i]=0;
for(pair<int,pii>p:vec)iss[p.S.F]=0;
}
ans=1;
for1(D.size()/2)ans=ans*2%mod;
cout<<ans<<endl;
}
