题解

So easy!

代码：

#include <bits/stdc++.h>
using namespace std;
int A[1005][1005];
int main(){
	int n,sum = 0;
	cin >> n;
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= n;j++){
			cin >> A[i][j];
			if(i == 1 || j == 1 || i == n || j == n){
				sum += A[i][j];
			}
		}
	}
	cout << sum;
	return 0;
}