/// @formatter:off
#include <bits/stdc++.h>
#include <experimental/iterator>
using namespace std;
#define overload3(_1, _2, _3, name, ...) name
#define rep1(n) for (decltype(n) _tmp = 0; _tmp < n; _tmp++)
#define rep2(i, n) for (decltype(n) i = 0; i < n; i++)
#define rep3(i, a, b) for (decltype(b) i = a; i < b; i++)
#define rep(...) overload3(__VA_ARGS__, rep3, rep2, rep1)(__VA_ARGS__)
struct IOSetup { IOSetup() noexcept { ios::sync_with_stdio(false); cin.tie(nullptr); cout << fixed << setprecision(10); cerr << fixed << setprecision(10); } } iosetup;
struct Print {
    ostream &os; const string sep; bool is_debug;
    Print(ostream &os, string sep, bool is_debug): os(os), sep(sep), is_debug(is_debug) {}
    void operator()(bool) { os << "\n"; }
    template<class Head, class... Tail> void operator()(bool is_first, Head &&head, Tail &&...tail) { os << head; if (not is_first and sizeof...(tail) != 0) os << sep; operator()(false, forward<Tail>(tail)...); }
    template<class T> void operator()(bool, vector<T> &vec) { copy(cbegin(vec), cend(vec), experimental::make_ostream_joiner(os, sep)); os << "\n"; }
    template<class T> void operator()(bool, vector<vector<T>> &vv) { size_t ind = 0; if (is_debug) os << "\n"; for (auto &vec: vv) { if (is_debug) os << ind++ << ": "; operator()(false, vec); } }
};
auto print_impl = Print(cout, " ", false);
#define print(...) print_impl(true, "", __VA_ARGS__)
#ifdef LOCAL
auto debug_impl = Print(cerr, " ", true);
#define debug(...) debug_impl(true, "(" #__VA_ARGS__ ") "s, __VA_ARGS__)
#else
#define debug(...)
#endif
template<class... T> void drop(const T &... x) { print(x...); exit(0); }
template <class T> bool chmax(T &a, const T &b) { return a < b and (a = b, true); }
template <class T> bool chmin(T &a, const T &b) { return a > b and (a = b, true); }
using i64 = long long;
using u64 = unsigned long long;
using f64 = long double;
// @formatter:on

size_t M = 2 * 1e5 + 10;

int main() {
    size_t n;
    cin >> n;
    vector<pair<int, int>> matrix(n);
    vector<pair<int, int>> hw(M, {0, 0});
    for (auto &&[hi, wi]: matrix) {
        cin >> hi >> wi;
        hw[hi].first++;
        hw[wi].second++;
    }
    int hcnt = 0, wcnt = 0;
    set<int> s{};
    rep(i, M) {
        const auto &[h, w] = hw[i];
        if (abs(h - w) >= 2) drop(0);
        else if (abs(h - w) == 1) {
            if (h > w) hcnt++;
            if (h < w) wcnt++;
        } else {
            assert(h == w);
            s.insert(h);
            s.insert(w);
        }
    }
    if (hcnt == wcnt) {
        if (hcnt == 0) print(size(s));
        else if (hcnt == 1)
            print(1);
        else
            print(0);
    } else
        print(0);
}