#include <bits/stdc++.h>
 
using namespace std;
using ll = long long;
 
const int N = 2e5 + 10;
 
struct Edge {
  int h, x, y, z;
} e[N];
struct SegTree {
  int l, r, cov, len;
} tr[N * 8];
 
int n, dce[N], dce_[N], dcnt, ally[N];
ll ans;
 
void pushup (int id) {
  //	tr[id].cov = min(tr[id * 2].cov, tr[id * 2 + 1].cov);
  if (tr[id].cov)
    tr[id].len = tr[id].r - tr[id].l;
  else
    tr[id].len = tr[id * 2].len + tr[id * 2 + 1].len;
}
 
void build (int id, int l, int r) {
  tr[id] = {dce_[l], dce_[r + 1]};
  if (l == r)
    return ;
  int mid = (l + r) >> 1;
  build(id * 2, l, mid), build(id * 2 + 1, mid + 1, r);
}
 
void modify (int id, int l, int r, int x, int y, int z) {
  if (x <= tr[id].l && tr[id].r <= y) {
    tr[id].cov += z, pushup(id);
    return ;
  }
  if (y < tr[id].l || tr[id].r < x)
    return ;
  int mid = (l + r) >> 1;
  modify(id * 2, l, mid, x, y, z), modify(id * 2 + 1, mid + 1, r, x, y, z);
  pushup(id);
}
 
int main () {
  ios::sync_with_stdio(0), cin.tie(0);
  cin >> n;
  for (int i = 1, x1, y1, x2, y2; i <= n; i++) {
    cin >> x1 >> y1 >> x2 >> y2, dce[i * 2 - 1] = x1, dce[i * 2] = x2;
    e[i * 2 - 1] = {y1, x1, x2, 1}, e[i * 2] = {y2, x1, x2, -1};
    ally[i * 2 - 1] = y1, ally[i * 2] = y2;
  }
  n *= 2, sort(dce + 1, dce + n + 1), sort(e + 1, e + n + 1, [](const Edge &i, const Edge &j){return i.h < j.h;}), sort(ally + 1, ally + n + 1), dce[0] = -1;
  for (int i = 1; i <= n; i++)
    if (dce[i] != dce[i - 1])
      dce_[++dcnt] = dce[i];
  build(1, 1, dcnt - 1);
  for (int i = 1, j = 1; i < n; i++) {
    for (; j <= n && e[j].h == ally[i]; j++)
      modify(1, 1, dcnt - 1, e[j].x, e[j].y, e[j].z);
    ans += 1ll * (ally[i + 1] - ally[i]) * tr[1].len;
  }
  cout << ans;
  return 0;
}