#include "bits/stdc++.h"
#pragma GCC optimize("Ofast")

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rep(i, b, e) for (intmax_t i = (b), i##_limit = (e); i < i##_limit; ++i)
#define reps(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__)

constexpr size_t    operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t  operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

template <class T, class Compare = less<>>
using MaxHeap = priority_queue<T, vector<T>, Compare>;
template <class T, class Compare = greater<>>
using MinHeap = priority_queue<T, vector<T>, Compare>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head&& head, Tail&&... tail) {
    cin >> head;
    input(forward<Tail>(tail)...);
}

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

inline void output() { cout << "\n"; }
template <class Head, class... Tail>
inline void output(Head&& head, Tail&&... tail) {
    cout << head;
    if (sizeof...(tail)) {
        cout << " ";
    }
    output(forward<Tail>(tail)...);
}

template <class T>
inline ostream& operator<<(ostream &os, const vector<T> &vec) {
    static constexpr const char *delim[] = {" ", ""};
    for (const auto &e: vec) {
        os << e << delim[&e == &vec.back()];
    }
    return os;
}

template <class T>
inline vector<T> makeVector(const T &initValue, size_t sz) {
    return vector<T>(sz, initValue);
}

template <class T, class... Args>
inline auto makeVector(const T &initValue, size_t sz, Args... args) {
    return vector<decltype(makeVector<T>(initValue, args...))>(sz, makeVector<T>(initValue, args...));
}

template <class Func>
class FixPoint : Func {
public:
    explicit constexpr FixPoint(Func&& f) noexcept : Func(forward<Func>(f)) {}

    template <class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const {
        return Func::operator()(*this, std::forward<Args>(args)...);
    }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept {
    return FixPoint<Func>{forward<Func>(f)};
}

template <class Container>
struct reverse_t {
    Container &c;
    reverse_t(Container &c) : c(c) {}
    auto begin() { return c.rbegin(); }
    auto end() { return c.rend(); }
};

template <class Container>
auto reversed(Container &c) {
    return reverse_t<Container>(c);
}

template <class T>
inline bool chmax(T &a, const T &b) noexcept {
    return b > a && (a = b, true);
}

template <class T>
inline bool chmin(T &a, const T &b) noexcept {
    return b < a && (a = b, true);
}

template <class T>
inline T diff(const T &a, const T &b) noexcept {
    return a < b ? b - a : a - b;
}
// End Header }}}

// Compress {{{
template <class T>
class Compress {
    vector<T> xs;

public:
    Compress() = default;

    Compress(const vector<T> &vs) {
        add(vs);
    }

    void add(const vector<T> &vs) {
        copy(vs.begin(), vs.end(), back_inserter(xs));
    }

    void add(const T &x) {
        xs.emplace_back(x);
    }

    void build() {
        sort(xs.begin(), xs.end());
        xs.erase(unique(xs.begin(), xs.end()), xs.end());
    }

    vector<intmax_t> get(const vector<T> &vs) const {
        vector<intmax_t> ret;
        transform(vs.begin(), vs.end(), back_inserter(ret), [&](const T &v) {
                return distance(xs.begin(), lower_bound(xs.begin(), xs.end(), v));
                });
        return ret;
    }

    unordered_map<T, intmax_t> dict() const {
        unordered_map<T, intmax_t> ret;
        for (intmax_t i = 0; i < xs.size(); ++i) {
            ret[xs[i]] = i;
        }
        return ret;
    }

    const size_t size() const {
        return xs.size();
    }

    const T &operator[](size_t k) const {
        return xs[k];
    }
};
// }}}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.setf(ios_base::fixed);
    cout.precision(10);
    var(size_t, N);
    vector<intmax_t> x1(N), y1(N), x2(N), y2(N);
    rep(i, 0, N) input(x1[i], y1[i], x2[i], y2[i]);
    Compress<intmax_t> X, Y;
    X.add(x1); X.add(x2);
    Y.add(y1); Y.add(y2);
    X.build(); Y.build();
    auto dx = X.dict(), dy = Y.dict();
    const size_t H = Y.size();
    const size_t W = X.size();
    auto mat = makeVector<intmax_t>(0, H, W);
    rep(i, 0, N) {
        mat[dy[y1[i]]][dx[x1[i]]]++;
        mat[dy[y1[i]]][dx[x2[i]]]--;
        mat[dy[y2[i]]][dx[x1[i]]]--;
        mat[dy[y2[i]]][dx[x2[i]]]++;
    }
    rep(y, 0, H - 1) rep(x, 0, W) mat[y + 1][x] += mat[y][x];
    rep(y, 0, H) rep(x, 0, W - 1) mat[y][x + 1] += mat[y][x];
    intmax_t res = 0;
    rep(y, 0, H - 1) rep(x, 0, W - 1) {
        if (mat[y][x]) res += (Y[y + 1] - Y[y]) * (X[x + 1] - X[x]);
    }
    output(res);
    return 0;
}



Measured memory_bytes: 128552