#include<bits/stdc++.h>
#define P(x,y) make_pair(x,y)
using namespace std;
class Rectangle{
    public:
    int x1 , y1 , x2 , y2;
    static Rectangle empt;
    Rectangle(){
        x1=y1=x2=y2=0;
    }
    Rectangle(int X1 , int Y1 , int X2 , int Y2){
        x1 = X1; y1=Y1;
        x2 = X2; y2=Y2;
    }
    Rectangle intersect(Rectangle R){
        if(R.x1 >= x2 || R.x2 <= x1) return empt;
        if(R.y1 >= y2 || R.y2 <= y1) return empt;
        return Rectangle(max(x1 , R.x1) , max(y1 , R.y1) , min(x2 , R.x2) , min(y2 , R.y2));
    }
};
struct Event{
    int x , y1 , y2 , type;
    Event(){}
    Event(int x , int y1 , int y2 , int type):x(x) , y1(y1) , y2(y2) , type(type){}
};
bool operator < (const Event&A , const Event&B){
    //if(A.x != B.x)
    return A.x < B.x;
    //if(A.y1 != B.y1) return A.y1 < B.y1;
    //if(A.y2 != B.y2()) A.y2 < B.y2;
}
const int MX=(1<<17);
struct Node{
    int prob , sum , ans;
    Node(){}
    Node(int prob , int sum , int ans):prob(prob) , sum(sum) , ans(ans){}
};
Node tree[MX*4];
int interval[MX];
void build(int x , int a , int b){
    tree[x] = Node(0 , 0 , 0);
    if(a==b){
        tree[x].sum+=interval[a];
        return;
    }
    build(x*2 , a , (a+b)/2);
    build(x*2+1 , (a+b)/2+1 , b);
    tree[x].sum = tree[x*2].sum + tree[x*2+1].sum;
}
int ask(int x){
    if(tree[x].prob) return tree[x].sum;
    return tree[x].ans;
}
int st , en , V;
void update(int x , int a , int b){
    if(st>b || en<a) return;
    if(a>=st && b<=en){
        tree[x].prob+=V;
        return;
    }
    update(x*2 , a , (a+b)/2);
    update(x*2+1 , (a+b)/2+1 , b);
    tree[x].ans = ask(x*2) + ask(x*2+1);
}
Rectangle Rectangle::empt = Rectangle();
vector < Rectangle > Rect;
vector < int > sorted;
vector < Event > sweep;
void compressncalc(){
    sweep.clear();
    sorted.clear();
    for(auto R : Rect){
        sorted.push_back(R.y1);
        sorted.push_back(R.y2);
    }
    sort(sorted.begin() , sorted.end());
    sorted.erase(unique(sorted.begin() , sorted.end()) , sorted.end());
    int sz = sorted.size();
    for(int j=0;j<sorted.size() - 1;j++)
        interval[j+1] = sorted[j+1] - sorted[j];
    for(auto R : Rect){
        sweep.push_back(Event(R.x1 , R.y1 , R.y2 , 1));
        sweep.push_back(Event(R.x2 , R.y1 , R.y2 , -1));
    }
    sort(sweep.begin() , sweep.end());
    build(1,1,sz-1);
}
long long ans;
void Sweep(){
    ans=0;
    if(sorted.empty() || sweep.empty()) return;
    int last = 0 , sz_ = sorted.size();
    for(int j=0;j<sweep.size();j++){
        ans+= 1ll * (sweep[j].x - last) * ask(1);
        last = sweep[j].x;
        V = sweep[j].type;
        st = lower_bound(sorted.begin() , sorted.end() , sweep[j].y1) - sorted.begin() + 1;
        en = lower_bound(sorted.begin() , sorted.end() , sweep[j].y2) - sorted.begin();
        update(1 , 1 , sz_-1);
    }
}
int main(){
//    freopen("in.in","r",stdin);
    int n;
    scanf("%d",&n);
    for(int j=1;j<=n;j++){
        int a , b ,c  , d;
        scanf("%d %d %d %d",&a,&b,&c,&d);
        Rect.push_back(Rectangle(a , b , c , d));
    }
    compressncalc();
    Sweep();
    cout<<ans<<endl;
}