#include <cassert>
#include <cstdio>
#include <cstring>
int a[51][51], f[110][51][51], m, n;
int max(int a, int b)
{
    return a > b ? a : b;
}
int main()
{
    memset(f, -1, sizeof(f));
    scanf("%d%d", &m, &n);
    for (int i = 1; i <= m; i++)
        for (int j = 1; j <= n; j++)
            scanf("%d", &a[i][j]);
    f[1][1][1] = 0;
    for (int i = 1; i <= n + m; i++)
        for (int j = 1; j <= m && j <= i; j++)
            for (int k = 1; k <= m && k <= i; k++)
                if (j != k || i == n + m)
                {
                    f[i][j][k] = max(f[i][j][k], f[i - 1][j][k]);
                    f[i][j][k] = max(f[i][j][k], f[i - 1][j - 1][k - 1]);
                    f[i][j][k] = max(f[i][j][k], f[i - 1][j - 1][k]);
                    f[i][j][k] = max(f[i][j][k], f[i - 1][j][k - 1]);
                    f[i][j][k] += a[j][i - j + 1] + a[k][i - k + 1];
                }
    printf("%d", f[n + m][m][m]);
    return 0;
}