摘苹果题解！！！

#include <iostream>
using namespace std;

const int MAXN = 1000;
int a[MAXN][MAXN];

int main() {
int n;
cin >> n;

for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
        cin >> a[i][j];
    }
}

long long ans = 0;
for (int i = 1; i < n - 1; ++i) {
    for (int j = 1; j < n - 1; ++j) {
        ans += a[i][j];
    }
    ans += a[i][0] + a[i][n - 1];
}
for (int j = 1; j < n - 1; ++j) {
    ans += a[0][j] + a[n - 1][j];
}

cout << ans << endl;

return 0;

}