#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true); }
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true); }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T> void debug(T L, T R) { while (L != R) cerr << *L << " \n"[next(L) == R], ++L; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
const int MAX_N = 1000010, p = 1e9 + 7;
int n;
pair<int,int> sh[MAX_N];
int atpos[MAX_N];
struct sgt {
int n;
vector<int> mx;
sgt (int n) : n(n) {
mx.resize(n<<1, -1);
}
void modify(int i, int v) {
i += n;
mx[i] = v;
for (;i>>=1;)
mx[i] = max(mx[i<<1], mx[i<<1|1]);
}
int qry(int l, int r) {
int res = -1;
l += n, r += n;
for (;l < r;l>>=1, r>>=1) {
if (l&1) chmax(res, mx[l++]);
if (r&1) chmax(res, mx[--r]);
}
return res;
}
sgt () {}
}tree;
bool valid (int i, int j) {
if (i > j) swap(i, j);
return sh[i].second < sh[j].first || sh[j].second < sh[i].second;
}
bool vis[MAX_N];
ll trykill(int x) {
vector<int> gp[2];
priority_queue<pair<int,int>, vector<pair<int,int>>, greater<pair<int,int>>> q;
q.emplace(x, 0);
while (q.size()) {
auto [x, g] = q.top(); q.pop();
gp[g].pb(x);
auto [l, r] = sh[x];
for (int j = x + 1;j < n;++j) if (!vis[j]) {
if (!valid(x, j)) {
q.emplace(j, g^1);
vis[j] = true;
}
}
// while (tree.qry(l, r) > r) {
// int tr = tree.qry(l, r);
// int id = atpos[tr];
// auto [cl, cr] = sh[id];
// q.emplace(id, g^1);
// tree.modify(cl, -1);
// }
}
auto allvalid = [&](vector<int> sid) {
for (int u : sid) for (int v : sid) if (u != v && !valid(u, v))
return false;
return true;
vector<int> stk;
for (int u : sid) {
auto [cl, cr] = sh[u];
while (stk.size()) {
auto [l, r] = sh[stk.back()];
if (cl < r && cr > r) return false;
if (cr < r) break;
stk.pop_back();
}
stk.pb(u);
}
return true;
};
// DE(x);
// debug(AI(gp[0]));
// debug(AI(gp[1]));
// cerr << endl;
//
for (int i = 0;i < 2;++i)
if (!allvalid(gp[i]))
return 0;
return 2;
}
int32_t main() {
ios_base::sync_with_stdio(0), cin.tie(0);
cin >> n;
for (int i = 0;i < n;++i) {
cin >> sh[i].first >> sh[i].second;
--sh[i].first, --sh[i].second;
}
if (n > 2000) return -1;
sort(sh, sh + n);
tree = sgt(n * 2);
for (int i = 0;i < n;++i) {
auto [l, r] = sh[i];
atpos[r] = atpos[l] = i;
tree.modify(l, r);
}
ll res = 1;
for (int i = 0;i < n;++i) {
auto [l, r] = sh[i];
if (vis[i]) continue;
//if (tree.qry(l, l+1) == -1) continue;
vis[i] = true;
tree.modify(l, -1);
res = res * trykill(i);
}
cout << res << '\n';
}
