'''
跟方格取数是一个题目，还是简单的DP
'''from functools import lru_cache# 两个人坐标分别为i1, k-i1 和i2, k-i2 时候的总最大收益
@lru_cache(typed=False, maxsize=128000000)
def dp(k, i1, i2):j1, j2 = k - i1, k - i2if k == 0:return grid[0][0]ans = 0for ii1, jj1, ii2, jj2 in [(i1 - 1, j1, i2 - 1, j2), (i1, j1 - 1, i2 - 1, j2), (i1 - 1, j1, i2, j2 - 1),(i1, j1 - 1, i2, j2 - 1)]:if ii1 >= 0 and ii1 < M and jj1 >= 0 and jj1 < N and ii2 >= 0 and ii2 < M and jj2 >= 0 and jj2 < N:val1 = grid[i1][j1]val2 = grid[i2][j2]total = val1 + val2 if i1 != i2 else val1ans = max(ans, dp(k - 1, ii1, ii2) + total)return ansM, N = list(map(int, input().split()))
grid = [None] * M
for i in range(M):grid[i] = list(map(int, input().split()))print(dp((M-1 + N-1), M - 1, M - 1))