Rectangle 2

Rectangle 2 ?

#include <iostream>
#include <cstdio>
using namespace std;
const int maxn = 101;
int main () {
	int n;
	cin >> n;
	int f[maxn][maxn];
	for (int i=0;i<=100;i++){
		for (int j=0;j<=100;j++){
			f[i][j]=0;
		}
	}
	for (int i=1;i<=n;i++){
		int x1,x2,y1,y2;
		cin >> x1;cin >> y1;cin >> x2;cin >> y2;
		for(int i=x1+1;i<=x2;i++){
			for (int j=y1+1;j<=y2;j++)f[i][j]=1;
			}
		}
	int a=0;
	for (int i=0;i<=maxn+1;i++){
		for (int j=0;j<=maxn+1;j++){
			if (f[i][j]==1)a=a+1;
		}
	}
	cout << a;
	return 0;
}