{

int m, n;

scanf("%d%d", &m, &n);

for(int i = 1; i <= m; i++)

for(int j = 1; j <= n; j++) scanf("%d", &a[i][j]);

#ifndef three

for(int x1 = 1; x1 <= m; x1++)

for(int y1 = 1; y1 <= n; y1++)

for(int x2 = 1; x2 <= m; x2++)

for(int y2 = 1; y2 <= n; y2++)

{

if(x1==x2 && y1==y2) continue;

int maxv = 0;

maxv = max(dp[x1-1][y1][x2-1][y2], max(dp[x1][y1-1][x2-1][y2], max(dp[x1][y1-1][x2][y2-1], dp[x1-1][y1][x2][y2-1])));

dp[x1][y1][x2][y2] = a[x1][y1]+a[x2][y2] + maxv;

//printf("dp[%d][%d][%d][%d] = %d\n", x1, y1, x2, y2, dp[x1][y1][x2][y2]);

}

//最后一次 x1 == x2 && y1 == y2

dp[m][n][m][n] = max(dp[m-1][n][m-1][n], max(dp[m][n-1][m-1][n], max(dp[m][n-1][m][n-1], dp[m-1][n][m][n-1])));

cout<<dp[m][n][m][n]<<endl;

#endif

#ifdef three

//三维dp

int dp[N+N][N][N];

for(int k = 1 ; k <= m + n - 1 ; k++ )

{

int t,s;

t = ( k > m ) ? m : k ;

s = ( k > n ) ? n : k ;

for( int x1 = k - s + 1 ; x1 <= t ; x1++ )

{

for(int x2 = k - s + 1 ; x2 <= t ; x2++ )

if( x1 != x2 || k == m + n - 1 )

{

int maxv = 0 ;

maxv = max(dp[k-1][x1][x2], max(dp[k-1][x1-1][x2], max(dp[k-1][x1][x2-1], dp[k-1][x1-1][x2-1])));

dp[k][x1][x2] = maxv + a[x1][k-x1+1]+a[x2][k-x2+1];

}

}

}

cout << dp[ m + n - 1 ][ m ][ m ] << endl ;

#endif

return 0;