#include<bits/stdc++.h>
using namespace std;
const int N=1e6+1314;
int n,sx[N],sy[N],ex[N],ey[N],x[N],y[N],ans;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>sx[i]>>sy[i]>>ex[i]>>ey[i];
		x[i]=sx[i];
		x[i+n]=ex[i];
		y[i]=sy[i];
		y[i+n]=ey[i];
	}
	sort(x+1,x+2*n+1);
	sort(y+1,y+2*n+1);
	for(int i=1;i<2*n;i++)
	for(int j=1;j<2*n;j++){
		for(int k=1;k<=n;k++){
			if(sx[k]<=x[i]&&x[i+1]<=ex[k]&&ey[k]<=y[j]&&y[j+1]<=sy[k]){
				ans+=(x[i+1]-x[i])*(y[j+1]-y[j]);
				break;
			}
		}
	}
	cout<<ans;
}
language
```


```