#include <bits/stdc++.h>
const int INF = 1e9, MOD = 1e9 + 7, ohara = 1e6;
const long long LINF = 1e18;
using namespace std;
long long n, cnt, ans, a, b, c, d, tmp, tmpp, m, h, w, x, y, sum, pos, k,
    l[ohara], r[ohara];
long double doua;
int dy[] = {1, 0, -1, 0};
int dx[] = {0, 1, 0, -1};
string alph("abcdefghijklmnopqrstuvwxyz"), s;
bool fl;
struct edge {
  int to, cost;
};
int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n;
  for (int(i) = 0; (i) < (int)(n); (i)++) cin >> l[i] >> r[i];
  sort(l, l + n);
  sort(r, r + n);
  for (int(i) = 0; (i) < (int)(n); (i)++) {
    ans += max(l[i], r[i]) + 1;
  }
  cout << (ans) << endl;
  return 0;
}
