Untitled

#include "bits/stdc++.h"
using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define debug(x...)
#endif

struct custom_hash {
    size_t operator()(vector<int32_t> const& vec) const {
        size_t seed = vec.size();
        for(auto& i : vec) {
            seed ^= i + 0x9e3779b9 + (seed << 6) + (seed >> 2);
        }
        return seed;
    }
};

void solve() {
    int n;
    cin >> n;
    vector<pair<int, int>> p(n);
    for (int i = 0; i < n; i++) {
        cin >> p[i].first >> p[i].second;
    }
    unordered_set<vector<int>, custom_hash> s;
    for (int i = 0; i < (1 << n); i++) {
        unordered_set<int> f;
        bool add = true;
        vector<int> value(n), cur(n);
        iota(cur.begin(), cur.end(), 0);
        for (int j = 0; j < n; j++) {
            if ((i >> j) & 1) {
                if (f.contains(p[j].first)) {
                    add = false;
                    break;
                }
                f.insert(p[j].first);
                value[j] = p[j].first;
            } else {
                if (f.contains(p[j].second)) {
                    add = false;
                    break;
                }
                f.insert(p[j].second);
                value[j] = p[j].second;
            }
        }
        if (!add) {
            continue;
        }
        sort(cur.begin(), cur.end(), [&](int lhs, int rhs) {
            return value[lhs] < value[rhs];
        });
        s.insert(cur);
    }
    cout << s.size();
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    int tests = 1;
    // cin >> tests;
    while (tests--) {
        solve();
    }
    return 0;
}