n = int(input().strip()) # 读取输入的正整数N matrix = [] # 创建一个空列表来存储矩阵 # 读取矩阵元素 for _ in range(n): row = list(map(int, input().strip().split())) matrix.append(row) # 初始化对角线之和为0 diagonal_sum = 0 # 遍历矩阵计算对角线之和 for i in range(n): for j in range(n): if i == j or i + j == n - 1: # 判断是否在对角线上 diagonal_sum += matrix[i][j] # 输出对角线之和 print(diagonal_sum)