#if __INCLUDE_LEVEL__ == 0

#include __BASE_FILE__

void Solve() {
  int n;
  IN(n);
  vector<int> x(n), y(n);
  for (int i : Rep(0, n)) {
    IN(x[i], y[i]);
  }

  int64_t ans = 0;
  vector<pair<int, int>> v{{0, 0}};
  for (int i : Rep(0, n)) {
    int last_x = INF;
    int last_y = INF;
    while (!(v.back().first <= x[i] && v.back().second <= y[i])) {
      tie(last_x, last_y) = v.back();
      v.pop_back();
    }
    if (last_x == INF) {
      assert(last_y == INF);
      if (v.back() != pair(x[i], y[i])) {
        ans += x[i] - v.back().first;
        ans += y[i] - v.back().second;
        v.emplace_back(x[i], y[i]);
      }
    } else {
      int x2 = min(x[i], last_x);
      int y2 = min(y[i], last_y);
      if (v.back() != pair(x2, y2)) {
        v.emplace_back(x2, y2);
      }
      if (v.back() != pair(x[i], y[i])) {
        ans += x[i] - x2;
        ans += y[i] - y2;
        v.emplace_back(x[i], y[i]);
      }
    }
  }
  OUT(ans);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  Solve();
}

#elif __INCLUDE_LEVEL__ == 1

#include <bits/stdc++.h>

template <class T> concept Range = std::ranges::range<T> && !std::convertible_to<T, std::string_view>;
template <class T> concept Tuple = std::__is_tuple_like<T>::value && !Range<T>;

namespace std {

istream& operator>>(istream& is, Range auto&& r) {
  for (auto&& e : r) is >> e;
  return is;
}
istream& operator>>(istream& is, Tuple auto&& t) {
  apply([&](auto&... xs) { (is >> ... >> xs); }, t);
  return is;
}

ostream& operator<<(ostream& os, Range auto&& r) {
  auto sep = "";
  for (auto&& e : r) os << exchange(sep, " ") << e;
  return os;
}
ostream& operator<<(ostream& os, Tuple auto&& t) {
  auto sep = "";
  apply([&](auto&... xs) { ((os << exchange(sep, " ") << xs), ...); }, t);
  return os;
}

}  // namespace std

using namespace std;

#define Rep(...) [](int l, int r) { return views::iota(min(l, r), r); }(__VA_ARGS__)
#define INF (INT_MAX / 2)
#define IN(...) (cin >> forward_as_tuple(__VA_ARGS__))
#define OUT(...) (cout << forward_as_tuple(__VA_ARGS__) << '\n')

#endif  // __INCLUDE_LEVEL__ == 1