#include <bits/stdc++.h>
#define int long long
#define all(x) x.begin(),x.end()
#define ff first
#define ss second
#define pb push_back
using namespace std;
bool check(vector <vector <int> > v){
stack <int> st;
for(auto x : v){
if(x[1]==0)st.push(x[2]);
else{
if(st.size()!=0 && st.top()==x[2])st.pop();
else return false;
}
}
return true;
}
signed main(){
ios_base::sync_with_stdio();
cin.tie(0);
int n;
cin>>n;
vector <pair <int,int> > v(n);
for(int i=0;i<n;i++){
cin>>v[i].ff>>v[i].ss;
}
int cnt=0;
for(int i=0;i<(1<<n);i++){
vector <vector <int> > gr1,gr2;
for(int j=0;j<n;j++){
if((i & (1<<j))!=0){
gr1.pb({v[j].ff,0,j});
gr1.pb({v[j].ss,1,j});
}
else{
gr2.pb({v[j].ff,0,j});
gr2.pb({v[j].ss,1,j});
}
}
sort(all(gr1));
sort(all(gr2));
if(check(gr1) && check(gr2))cnt++;
}
cout<<cnt<<"\n";
}
/*
0 2 1
0 4 2
0 6 3
1 5 1
1 7 3
1 8 2
0 2 1
1 5 1
*/
