n,m = map(int,input().split())

f = [[[0 for _ in range(n)] for _ in range(n)] for _ in range(m+n-1)]
g = []
for _ in range(n):
    t = list(map(int, input().split()))
    g.append(t)

for k in range(m+n-1):
    for x1 in range(n):
        for x2 in range(n):
            y1 = k-x1
            y2 = k-x2
            if y1 >= 0 and y2 >= 0 and y1 <m and y2 <m:
                w = g[x1][y1]
                if y1 != y2 :
                    w += g[x2][y2]
                f[k][x1][x2] = max(f[k][x1][x2], f[k-1][x1-1][x2] + w)
                f[k][x1][x2] = max(f[k][x1][x2], f[k-1][x1-1][x2-1] + w)
                f[k][x1][x2] = max(f[k][x1][x2], f[k-1][x1][x2-1] + w)
                f[k][x1][x2] = max(f[k][x1][x2], f[k-1][x1][x2] + w)

print(f[m+n-2][n-1][n-1])