def diagonal_sum(matrix, n): main_diagonal_sum = 0 secondary_diagonal_sum = 0 for i in range(n): main_diagonal_sum += matrix[i][i] # 主对角线元素 secondary_diagonal_sum += matrix[i][n - 1 - i] # 次对角线元素 return main_diagonal_sum + secondary_diagonal_sum # 读取输入 n = int(input()) matrix = [] for _ in range(n): row = list(map(int, input().split())) matrix.append(row) # 计算对角线之和 sum_of_diagonals = diagonal_sum(matrix, n) # 输出对角线之和 print(sum_of_diagonals)