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#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <bitset>
#include <assert.h>

using namespace std;
typedef long long ll;
typedef set<int>::iterator ssii;

#define Cmp(a, b) memcmp(a, b, sizeof(b))
#define Cpy(a, b) memcpy(a, b, sizeof(b))
#define Set(a, v) memset(a, v, sizeof(a))
#define debug(x) cout << #x << ": " << x << endl
#define _forS(i, l, r) for(set<int>::iterator i = (l); i != (r); i++)
#define _rep(i, l, r) for(int i = (l); i <= (r); i++)
#define _for(i, l, r) for(int i = (l); i < (r); i++)
#define _forDown(i, l, r) for(int i = (l); i >= r; i--)
#define debug_(ch, i) printf(#ch"[%d]: %d\n", i, ch[i])
#define debug_m(mp, p) printf(#mp"[%d]: %d\n", p->first, p->second)
#define debugS(str) cout << "dbg: " << str << endl;
#define debugArr(arr, x, y) _for(i, 0, x) { _for(j, 0, y) printf("%c", arr[i][j]); printf("\n"); }
#define _forPlus(i, l, d, r) for(int i = (l); i + d < (r); i++)
#define lowbit(i) (i & (-i))
#define MPR(a, b) make_pair(a, b)

pair<int, int> crack(int n) {
    int st = sqrt(n);
    int fac = n / st;
    while (n % st) {
        st += 1;
        fac = n / st;
    }

    return make_pair(st, fac);
}

inline ll qpow(ll a, int n) {
    ll ans = 1;
    for(; n; n >>= 1) {
        if(n & 1) ans *= 1ll * a;
        a *= a;
    }
    return ans;
}

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

ll gcd(ll a, ll b) {
    return b == 0 ? a : gcd(b, a % b);
}

ll ksc(ll a, ll b, ll mod) {
    ll ans = 0;
    for(; b; b >>= 1) {
        if (b & 1) ans = (ans + a) % mod;
        a = (a * 2) % mod;
    }
    return ans;
}

ll ksm(ll a, ll b, ll mod) {
    ll ans = 1 % mod;
    a %= mod;

    for(; b; b >>= 1) {
        if (b & 1) ans = ksc(ans, a, mod);
        a = ksc(a, a, mod);
    }

    return ans;
}

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

bool _check(int x) {
    //
    return true;
}

int bsearch1(int l, int r) {
    while (l < r) {
        int mid = (l + r) >> 1;
        if(_check(mid)) r = mid;
        else l = mid + 1;
    }
    return l;
}

int bsearch2(int l, int r) {
    while (l < r) {
        int mid = (l + r + 1) >> 1;
        if(_check(mid)) l = mid;
        else r = mid - 1;
    }
    return l;
}

template<class T>
bool lexSmaller(vector<T> a, vector<T> b) {
    int n = a.size(), m = b.size();
    int i;
    for(i = 0; i < n && i < m; i++) {
        if (a[i] < b[i]) return true;
        else if (b[i] < a[i]) return false;
    }
    return (i == n && i < m);
}

// ============================================================== //

const int maxn = 1e4 + 10;
int n, m[2];

class A {
public:
    int x, y1, y2, c;
    A() = default;
    A(int x, int y1, int y2, int c) : x(x), y1(y1), y2(y2), c(c) {}

    bool operator< (const A &rhs) const {
        return x < rhs.x || (x == rhs.x && c < rhs.c);
    }
} a[2][maxn];

vector<int> B[2];
map<int, int> ny[2];

void prework() {
    _for(i, 0, 2) {
        sort(a[i]+1, a[i]+1+m[i]);
        sort(B[i].begin(), B[i].end());
        B[i].erase(unique(B[i].begin(), B[i].end()), B[i].end());

        for (auto x : B[i]) ny[i][x] = lower_bound(B[i].begin(), B[i].end(), x) - B[i].begin();
    }
}

class segTree {
public:
    int l, r;
    int cnt;
    bool fl, fr;
    int cover;

    void clear() {
        l = r = 0;
        cnt = 0;
        fl = fr = false;
        cover = 0;
    }
} tr[maxn * 4];

void build(int p, int l, int r) {
    tr[p].clear();
    tr[p].l = l; tr[p].r = r;

    if (l == r) return;

    int mid = (l + r) >> 1;
    build(p<<1, l, mid);
    build(p<<1 | 1, mid + 1, r);
}

void pushup(int p, int sgn) {
    if (tr[p].cover) {
        tr[p].cnt = 1;
        tr[p].fl = tr[p].fr = 1;
    }
    else {
        if (tr[p].l == tr[p].r) {
            tr[p].fl = tr[p].fr = 0;
            tr[p].cnt = 0;
        }
        else {
            tr[p].fl = tr[p<<1].fl;
            tr[p].fr = tr[p<<1 | 1].fr;

            tr[p].cnt = tr[p<<1].cnt + tr[p<<1 | 1].cnt;
            if (tr[p<<1].fr && tr[p<<1 | 1].fl) tr[p].cnt--;
        }
    }
}

void change(int p, int l, int r, int v, int sgn) {
    if (l <= tr[p].l && tr[p].r <= r) {
        tr[p].cover += v;
        pushup(p, sgn);
        return;
    }

    int mid = (tr[p].l + tr[p].r) >> 1;
    if (l <= mid) change(p<<1, l, r, v, sgn);
    if (r > mid) change(p<<1 | 1, l, r, v, sgn);
    pushup(p, sgn);
}

int solve(int sgn) {
    build(1, 0, B[sgn].size() - 2);
    int ans = 0;

    _rep(i, 1, m[sgn]) {
        change(1, ny[sgn][a[sgn][i].y1], ny[sgn][a[sgn][i].y2]-1, a[sgn][i].c, sgn);
        //debug(ny[a[i].y1]);
        ans += 2 * tr[1].cnt * (a[sgn][i+1].x - a[sgn][i].x);
    }
    return ans;
}

int ans = 0;
void init() {
    memset(m, 0, sizeof(m));
    _for(i, 0, 2) {
        B[i].clear();
        ny[i].clear();
    }
    ans = 0;
}

int main() {
    //freopen("input.txt", "r", stdin);
    while (~scanf("%d", &n)) {
        init();

        _rep(i, 1, n) {
            int x1, y1, x2, y2;
            scanf("%d%d%d%d", &y1, &x1, &y2, &x2);
            a[0][++m[0]] = A(x1, y1, y2, 1);
            a[0][++m[0]] = A(x2, y1, y2, -1);
            B[0].push_back(y1);
            B[0].push_back(y2);

            a[1][++m[1]] = A(y1, x1, x2, 1);
            a[1][++m[1]] = A(y2, x1, x2, -1);
            B[1].push_back(x1);
            B[1].push_back(x2);
        }
        assert(m[0] == n*2 && m[1] == n*2);

        // prework
        prework();
        _for(i, 0, 2) ans += solve(i);
        printf("%d\n", ans);
    }
}