#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

template <class T> std::istream& operator>>(std::istream& is, std::vector<T>& v) {
    for (auto& e : v) {
        is >> e;
    }
    return is;
}

template <class T> std::ostream& operator<<(std::ostream& os, const std::vector<T>& v) {
    for (std::string_view sep = ""; const auto& e : v) {
        os << std::exchange(sep, " ") << e;
    }
    return os;
}

template <class T, class U = T> bool chmin(T& x, U&& y) {
    return y < x and (x = std::forward<U>(y), true);
}

template <class T, class U = T> bool chmax(T& x, U&& y) {
    return x < y and (x = std::forward<U>(y), true);
}

template <class T> void mkuni(std::vector<T>& v) {
    std::ranges::sort(v);
    auto result = std::ranges::unique(v);
    v.erase(result.begin(), result.end());
}

template <class T> int lwb(const std::vector<T>& v, const T& x) {
    return std::distance(v.begin(), std::ranges::lower_bound(v, x));
}

using namespace std;

using ll = long long;

bool check(pair<int, int> s, pair<int, int> t) { return s.first <= t.first and s.second <= t.second; }

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);

    int N;
    cin >> N;
    stack<pair<int, int>> st;
    st.emplace(0, 0);
    ll ans = 0;
    for (; N--;) {
        int X, Y;
        cin >> X >> Y;
        if (check(st.top(), {X, Y})) {
            auto p = st.top();
            ans += (X + Y) - (p.first + p.second);
            st.emplace(X, Y);
        } else {
            pair<int, int> pre;
            while (not check(st.top(), {X, Y})) {
                pre = st.top();
                st.pop();
            }
            int nx = min(X, pre.first), ny = min(Y, pre.second);
            ans += (X + Y) - (nx + ny);
            st.emplace(nx, ny);
            st.emplace(X, Y);
        }
    }

    cout << ans << "\n";
    return 0;
}