#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
struct Node
{
int l, r;
int len, lazy;
}tr[N];
struct Segment
{
int x;
int y1;
int y2;
int flag;
bool operator<(Segment p)
{
return x < p.x;
}
}a[N];
void pushup(int u)
{
if(tr[u].lazy) tr[u].len = tr[u].r - tr[u].l + 1;
else tr[u].len = tr[u << 1].len + tr[u << 1 | 1].len;
}
void bulid(int u, int l, int r)
{
if(l == r) tr[u] = {l, r};
else
{
tr[u] = {l, r};
int mid = l + r >> 1;
bulid(u << 1, l, mid);
bulid(u << 1 | 1, mid + 1, r);
}
}
void modify(int u, int l, int r, int flag)
{
if(l <= tr[u].l && tr[u].r <= r)
{
tr[u].lazy += flag;
pushup(u);
}
else
{
int mid = tr[u].l + tr[u].r >> 1;
if(l <= mid) modify(u << 1, l, r, flag);
if(r > mid) modify(u << 1 | 1, l, r, flag);
pushup(u);
}
}
int main()
{
int n;
cin >> n;
int cnt = 0;
for(int i = 1; i <= n; i ++ )
{
int x1, x2, y1, y2;
scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
a[ ++ cnt] = {x1, y1, y2, 1};
a[ ++ cnt] = {x2, y1, y2, -1};
}
bulid(1, 0, 10010);
sort(a + 1, a + cnt + 1);
int ans = 0;
for(int i = 1; i <= cnt; i ++ )
{
if(i != 1) ans += tr[1].len * (a[i].x - a[i - 1].x);
modify(1, a[i].y1, a[i].y2 - 1, a[i].flag);
}
cout << ans;
}