7. 사과나무

# 사과나무 (다이아몬드)

def run(N, mp):
    tot = 0
    s = e = N//2
    for i in range(N):
        for j in range(s, e+1):
            tot += mp[i][j]

        if i < N//2:
            s -= 1
            e += 1
        else:
            s += 1
            e -= 1

    return tot


N = int(input())
mp = [list(map(int, input().split())) for _ in range(N)]
print(run(N, mp))