#include <bits/stdc++.h>
#define F first
#define S second
using namespace std;
const int N = 2e6 + 10 , mod = 1e9 + 7;
int n , R[N];
pair <int , int> a[N];
set <pair<int , int>> st;
struct DSU{
set <int> st[N];
int root[N];
void Build()
{
for(int i = 0 ; i < n ; i++)
{
st[a[i].F].insert(a[i].S);
root[a[i].S] = a[i].F;
}
}
void Merge(int a , int b)
{
//cout << a << " MErge " << b << endl;
n--;
if(st[a].size() > st[b].size())
swap(a , b);
for(auto u : st[a])
{
st[b].insert(u);
root[u] = b;
}
}
}dsu;
bool Check_Bipartite()
{
bool res = true;
vector <int> A , B;
A.push_back(mod);
B.push_back(mod);
for(int i = 1 ; i <= 2 * n ; i++)
{
if(R[i] == 0)
{
if(A.back() == i)
A.pop_back();
else if(B.back() == i)
B.pop_back();
else
res = false;
}
else
{
if(A.back() < R[i] || (B.back() < A.back() && B.back() > R[i]))
B.push_back(R[i]);
else
A.push_back(R[i]);
}
}
return res;
}
signed main()
{
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
cin >> n;
int fn = n;
for(int i = 0 ; i < n ; i++)
cin >> a[i].F >> a[i].S;
for(int i = 0 ; i < n ; i++)
{
//cout << a[i].F << " " << a[i].S << endl;
R[a[i].F] = a[i].S;
}
if(!Check_Bipartite())
{
cout << 0 << '\n';
return 0;
}
dsu.Build();
for(int i = 1 ; i <= 2 * fn ; i++)
{
/*cout << i << " WTF " << endl;
for(auto u : st)
cout << u.F << " " << u.S << endl;*/
if(R[i] == 0)
{
auto now = *st.begin();
if(now.F != i)
continue;
st.erase(now);
dsu.st[now.S].erase(now.F);
if(!dsu.st[now.S].empty())
st.insert({*dsu.st[now.S].begin() , now.S});
}
else
{
//cout << i << " " << R[i] << endl;
while(!st.empty() && (*st.begin()).F < R[i])
{
dsu.Merge(dsu.root[R[i]] , (*st.begin()).S);
st.erase(st.begin());
}
st.insert(make_pair(*dsu.st[dsu.root[R[i]]].begin() , dsu.root[R[i]]));
}
}
int ans = 1;
for(int i = 0 ; i < n ; i++)
ans = (ans + ans) % mod;
cout << ans << '\n';
return 0;
}
