import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int s = 0 ;
		int[][] a = new int[n][n];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				a[i][j] = sc.nextInt();
			}
		}
		for (int i = 0; i < n; i++) {
				s = s + a[i][i];
				s = s + a[i][n-i-1];
		}
		System.out.println(s);

	}
}
/**************************************************************
	Problem: 1726
	User: admin
	Language: Java
	Result: Accepted
	Time:2379 ms
	Memory:40300 kb
****************************************************************/