def sum_of_diagonals(matrix): n = len(matrix) main_diagonal_sum = 0 secondary_diagonal_sum = 0 for i in range(n): main_diagonal_sum += matrix[i][i] secondary_diagonal_sum += matrix[i][n-i-1] return main_diagonal_sum + secondary_diagonal_sum n = int(input()) matrix = [] for _ in range(n): row = list(map(int, input().split())) matrix.append(row) result = sum_of_diagonals(matrix) print(result)