#include <bits/stdc++.h>
using namespace std;
template <class T>
using vv = vector<vector<T>>;
template <class T>
ostream &operator<<(ostream &os, const vector<T> &t) {
  os << "{";
  for (int(i) = 0; (i) < (t.size()); ++(i)) {
    os << t[i] << ",";
  }
  os << "}" << endl;
  return os;
}
template <class T, size_t n>
ostream &operator<<(ostream &os, const array<T, n> &t) {
  os << "{";
  for (int(i) = 0; (i) < (n); ++(i)) {
    os << t[i] << ",";
  }
  os << "}" << endl;
  return os;
}
template <class S, class T>
ostream &operator<<(ostream &os, const pair<S, T> &t) {
  return os << "(" << t.first << "," << t.second << ")";
}
template <class S, class T, class U>
ostream &operator<<(ostream &os, const tuple<S, T, U> &t) {
  return os << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ")";
}
template <class S, class T, class U, class V>
ostream &operator<<(ostream &os, const tuple<S, T, U, V> &t) {
  return os << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ","
            << get<3>(t) << ")";
}
template <class S, class T, class U, class V, class W>
ostream &operator<<(ostream &os, const tuple<S, T, U, V, W> &t) {
  return os << "(" << get<0>(t) << "," << get<1>(t) << "," << get<2>(t) << ","
            << get<3>(t) << "," << get<4>(t) << ")";
}
template <class T>
inline bool MX(T &l, const T &r) {
  return l < r ? l = r, 1 : 0;
}
template <class T>
inline bool MN(T &l, const T &r) {
  return l > r ? l = r, 1 : 0;
}
const long long MOD = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(0);
  int n;
  cin >> n;
  vector<int> ls(n), rs(n);
  for (int(i) = 0; (i) < (n); ++(i)) cin >> ls[i] >> rs[i];
  sort((ls).begin(), (ls).end());
  sort((rs).begin(), (rs).end());
  long long re = 0;
  for (int(i) = 0; (i) < (n); ++(i)) re += max(ls[i], rs[i]) + 1;
  cout << re << endl;
  return 0;
}
